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    • 专利摘要:
    The invention relates to a method for determining snow parameters of a snow cover (S) arranged on a ground (G), comprising the phases that in an initialization phase without snow cover (S) on the bottom (G) and with at least one antenna (A1 ) of the at least two antennas (A1, A2) the relative position between the two antennas (A1, A2) of the at least two antennas (A1, A2) connected to the two receivers by means of received microwave signals from navigation satellites from differential pseudo-orange measurements and carrier phase measurements determines the relative position between the two antennas (A1, A2) and performs parallel reference measurements on signal strength; it is decided in at least one decision phase whether it is wet or dry snow; in at least one measurement phase at least one time at which a snowpack (S) covers the ground (G) and one antenna (A1) of the at least two antennas (A1, A2), the snow-related propagation delay in the zenith direction and the integer ambiguities the double-differential carrier phase measurements determined using the initial phase derived relative position and performs parallel measurements of signal strength; In at least one result determination phase, at least one of the snow parameters snow water equivalent, snow depth and snow moisture of the snow cover (S) arranged on the ground (G) is determined at least one time.
    公开号:CH712623A2
    申请号:CH00827/17
    申请日:2017-06-23
    公开日:2017-12-29
    发明作者:Koch Franziska；Mauser Wolfram；Appel Florian；henkel Patrick
    申请人:Advanced Navigation Solutions ANavS GmbH；
    IPC主号:
    专利说明:

    Description [0001] The invention relates to a method for determining snow parameters. In particular, the invention relates to a method for determining snow parameters using microwave signals from one or more global navigation satellite systems (GNSS).
    Background Art It is known that signals from navigation satellites in the L-band microwave range are transmitted at a frequency between 1 and 2 GHz and can be received by GNSS receivers. From the navigation satellite signals, GNSS receivers derive measurements of carrier phase, pseudorange, and signal strength.
    The carrier phase measurement involves the phase relationship of the sinusoidal carrier signal measured at the receiver, which is dependent on the distance between satellite and receiver, atmospheric delays and clock errors in navigation satellites and receivers. This carrier phase measurement is continuously determined in the receiver with a control loop (Phase Locked Loop, PLL), which minimizes the deviation between measured and receiver-generated phase position.
    The pseudorange measurement represents an estimate of the distance between satellite and receiver. This pseudorange is determined from the transit time of the signal between satellite and receiver with another loop (delay locked loop, DLL). The carrier phase and pseudo orange measurements are the input quantities of the real time kinematic positioning (RTK) [1, 2].
    The signal strength measurement is expressed as the ratio between the received signal power and the carrier-to-noise power density ratio (C / N0). This is also determined in the control loops by integration / accumulation of the received signal strength. The signal strength measurement is reduced by the liquid water content of the snow, since in the microwave range, the dielectric properties between air and water differ significantly.
    By processing GNSS raw data, such as pseudorange and carrier phase measurements, using RTK positioning algorithms, the position of a GNSS antenna, even with low cost single frequency GNSS receivers, can be precisely determined in the millimeter to centimeter range become [3-6]. This allows accurate relative run-time determination between such GNSS receivers and a set of global navigation satellites. The quality depends on the availability and elevation of the navigation satellites within the visible range of the GNSS receiver. This applies to various local and global systems of navigation satellites (e.g., GPS, GLONASS, Galileo, BeiDou, QZSS, GAGAN) and their combination [7, 8].
    It is further known that the propagation speed of electromagnetic microwave signals in the snow (in the dry state in proportions of ice crystals and air, in the wet state additionally consisting of water) and also in most other in nature occurring media is smaller than in the air or in vacuum. Both the attenuation of the signals as well as their reflection and refraction as well as the change in the signal propagation speed depend on the dielectric properties of the snow as well as the density and moisture content of the respective snowpack [9-11]. Snow parameters can thus be determined by the interaction of electrical microwave signals with a medium such as snow.
    In the context of the method according to the invention, the term "snow parameter" includes at least the snow water equivalent (SWE) of a snowpack which describes the entire water stored in the snowpack in liquid and solid form in the vertical direction Snow height ("height of snow", HS) of a snow cover in vertical direction and the snow light (proportion of liquid water in the snow cover, "LWC") of a snow cover in the vertical direction. The term snow cover refers to the local expression of the presence of snow in one place. The snow parameters determined by the method are assumed to be homogeneous for the area in the snowpack, which is penetrated by all navigation satellite signals.
    Schmid et al. [12] describe the running time delay of L-band microwave signals in snow, measured with an upward-looking ground radar at 1.6 GHz. In this method, in the presence of a snow cover over the ground, from a radar installed in the ground but facing towards the sky, L-band signals are emitted into the snowpack and markedly reflected at the interface between snow surface and atmosphere. The antennas of this radar record the two-way runtime of the signals through the snowpack. On the basis of an assumption of the snow density (SD) (quotient of the mass and volume of the snow cover) and the application of dielectric snow models, the snow depth (HS) could be deduced under dry snow conditions [12], with knowledge of the snow density (SD), moreover together with the calculated snow depth (HS), the snow water equivalent (SWE), as a quotient of snow depth (HS) and snow density (SD) are determined [12], the snow density (SD) can either measured, modeled [12] or eg estimated according to [13] and / or [14]. Overall, however, deviations in the density determination have only minor effects [15].
    In wet snow, the calculation of snow parameters is more complex, since in addition to the propagation delay and the signal attenuation by the occurrence of liquid water must be considered [10]. Koch et al.
    [15] using GPS signal strength data for the first time, continuously monitored snow snow cover (LWC) throughout the spring snowmelt periods mathematically and physically using a non-destructive method together with dielectric snowmaking models [11], externally measured snow depth data, and an assumption derived from the snow density (HS).
    To determine the signal strength attenuation at least one GPS antenna was placed on the ground under the snow cover [15, 16]. In combination with measurements of the propagation delay in snow, measured with an L-band ground radar, the snow depth (HS) and the snow water equivalent (SWE) could be determined for both dry and wet snow [16]. The combination of GNSS sensors with ground radars, however, leads to an overall high cost due to the higher cost of radar equipment. In addition, the latter have a high power consumption and are expensive to install. Thus, this approach is unsuitable for large, dense sensor networks and their operation in remote locations. In contrast, the GNSS sensors used are available at low cost; their chips are e.g. also installed in smartphones as components. GNSS sensors are capable of accepting the receiver function in low-cost, reliable, independent-of-energy, high-bandwidth systems for determining snow parameters.
    Furthermore, it is known that so far in particular expensive, geodetic multi-frequency GNSS receivers (consisting of a high-quality clock quartz and a synchronous processing of the signals at different frequencies) and antennas (with multipath suppression) tested for the detection of snow parameters snow depth (HS) was determined by reflectometry. In this method, at least one GNSS antenna is located above the snowpack to receive both the direct and the snow surface reflected GNSS signals (e.g., [16-18]). Depending on how much snow lies, the reflected signals change, from which the snow depth can be derived. However, this technique can not determine the liquid water content and the snow water equivalent (SWE) only indirectly [19]. In addition, these high-end GNSS receivers are very expensive compared to the low-cost products and thus not rebuild sensor networks, e.g. in alpine and remote regions, suitable. In addition, wide, free and flat areas of about 1000 m2 are needed for the GNSS reflectometry technique [19, 20], which is used, for example. hardly to be found in alpine space.
    Furthermore, other mechanical, acoustic, optical but also electronic measurement techniques for determining individual snow parameters are known. However, these are not able to measure several snow parameters in parallel with a simple measuring principle and a simple device.
    The above statements are based on the following prior art: [1] N.C. Talbot, Centimeters xnthè Field, A users Perspective of Real-Time Kinematic Positioning in a Production Environment, Proc, of the 6th Int. Techn. Meet. of the Satellite Div. of the Inst, of Navigation (ION GPS), Salt Lake City, UT, USA, 1049-1057.1993.
    T. Takasu and A. Yasuda, Development of the low-cost RTK-GPS receivers RTKLIB, Proc, of Int. Symp. On GPS / GNSS., Jeju, Korea, 2009.
    [3] P. Henkel, Tightly coupled precise point positioning and attitude decision making, IEEE Transactions on Aerospace and Electronic Systems, 51 (4), 3182-3197, 2015.
    [4] P. Henkel, and C. Günther, Partial integer decorrelation: Optimum trade-off between variance production and bias amplification, Journal of Geodesy, 84 (1), 51-63, 2010.
    [5] P. Henkel, M. lafrancesco and A. Speri, Precise Point Positioning with Multipath Estimation, Proc, of ION / IEEE Position, Location and Navigation Symp. (PLANS), Savannah, GA, USA, 6 pp., 2016 ,
    [6] P. Henkel, and J. Cärdenas, Method for Determining a Baseline between Two Receivers, patent App. No .: EP 12199 772.0, appi, date: 28.12.2012; European publication no. EP2749900 (AI), publication date: 02.07.2014.
    [7] P. Henkel, U. Mittmann and M. Lafrancesco, Real-Time Kinematic Positioning with GPS and GLONASS, Proc. of 24-th Europ. Signal Proc. Conf. (EÜSIPCO), Budapest, Hungary, 5 pp., 2016.
    [8] N. Kubo, F. Wu, and A. Yasuda, Integral GPS and QZSS Ambiguity Resolution, Transactions Jap. Soc. Aero. Space Be., Voi. 47, no. 155, 38-43, 2004.
    [9] F.T, Ulaby, D.G. Long, W.J. Blackwell, C. Elachi, A.K. Fung, C. Ruf, K. Sarabandi, H.A. Zebker, and J. Van Zyl, Microwave Radar and Radiometry Remote Sensing, 2014.
    [10] J.H. Bradford, J.T. Harper, and J. Brown, Complex dielectric permittivity measurements for ground-penetrating radar data to estimate snow liquid water content in the pendular regime, Water Resources Research, 45, W08403, 2009.
    [11] Μ. E. Tiuri, A.H. Sihvola, E.G. Nyfors, and Μ. T. Hallikainen, The Complex Constant Constant of Snow at Micro-wave Frequencies, IEEE Journal of Oceanic Engineering, 9 (5), 377-382, 1984.
    [12] L. Schmid, A. Heilig, C. Mitterer, J. Schweizer, H. Maurer, R. Okorn and O. Eisen, Continuous snowpack monitoring using upward-looking ground-penetrating radar technology, Journal of Glaciology, 60, 221, 509-525, 2014.
    [13] V, B. Meloysund, Leira, K.V. Heiseth, and K.R. Lise, Predicting snow density using meteorological data, Meteo-rological Applications, 14 (4), 413-423, 2007.
    [14] T.C. Jonas, Marty, and J. Magnusson (2009), Estimating the snow water equivalent from snow depth measure-ments in the Swiss Alps, Journal of Hydrology, 378 (1), 161-167.
    [15] F. Koch, M. Prasch, L. Schmid, J. Schweizer, and W. Mauser, Measuring snow liquid water content with low-cost GPS receivers, Sensors, 14 (11), 20975-20999, 2014.
    [16] L. Schmid, F. Koch, A. Heilig, M. Prasch, 0. Eisen, W. Mauser and J. Schweizer, A novel sensor combination (upGPR-GPS) to continuously and nondestructively derive snow cover properties, Geophysical Research Lettere, 42 (9), 3397-34052015.
    [17] K. M. Larson, E. Gutmann, V. Zavorotny, J. Braun, M. Williams and F. Nievinski, Can we measure snow depth with GPS receivers Geophysical Research Lettere, 36 (17), L17 502, 2009.
    [18] S. Jin, N. Naj ibi, Sensing snow height and surface temperature variations in Greenland from GPS reflected Signals, Advances in Space Research, 53 (11), 1623-1633, 2014.
    [19] N. Rodriguez-Alvarenz, E. Valencia, X. Bosch-Lluis, A Camps, I. Ramos-Perez, H. Park, and M. Vall-Llossera, Snow thickness monitoring using GNSS measurements, Geoscience and Remote Sensing Lettere, IEEE, 9 (6), 1109-1113, 2012.
    [20] JL McCreight, EE Small, and KM Larson, Snow Depth, density, and SWE estimates derived from GPS re-listing data: Validation in the Western US, Water Resources Research, 50 (8), 6892-6909, , 2014.
    [21] K.M. Larson, GPS interferometric reflectometry: applications to surface soil moisture, snow depth, and vegetation water content in the Western United States, Wiley Interdisciplinary Reviews: Water, 3 (6), 775-787, 2016.
    OBJECT AND OBJECT In view of the disadvantages of the prior art described above, it was an object of the present invention to provide a new method for determining the snow parameters snow water equivalent (SWE), snow height (HS) and snow (LWC).
    In particular, it was an object of the present invention to provide a method for determining the snow parameters snow water equivalent (SWE), snow depth (HS) and snow (LWC), which can work with easily available, inexpensive equipment and free accessible raw data, ideally over an existing communication network can be generated and transmitted to the receiver.
    It was another object of the present invention to provide a method for determining the snow parameters snow water equivalent (SWE), snow depth (HS) and snow (LWC) that even in remote regions, especially in regions without external power supply, by using a corresponding device can be implemented while still delivering reliable, fast-access results.
    An apparatus for determining snow parameters that can be used for the method according to the present invention is described in a co-pending patent application of the present inventors entitled "Apparatus for Determining Snow Parameters". SOLUTION OF THE PROBLEM The above and other objects of the invention, ie to determine the desired snow parameters, are possible with a mathematical and physical derivation of quantities from the raw data of GNSS signals received over a period of time.
    As already stated in the description of the prior art, microwave signals in the snow u.a. Refraction, damping and propagation delays. In general, for calculating snow parameters, microwave signals influenced by the dielectric properties of a snowpack can be used, which in the case of GNSS signals are carrier phase, pseudo orange and signal strength measurements.
    The GNSS signal propagation in the microwave range is determined by the dielectric properties of a medium and thus differs between air and snow. The propagation speed is due to the
    Snow reduces so that the carrier phase and pseudo orange measurements are effectively delayed. The dielectric properties of snow or the reduction of the propagation velocity with respect to the speed of light in vacuum depend on the moisture content and the density of the snowpack [10, 11]. In addition, the GNSS signals are refracted when entering the snow surface, whereby the strength of the refraction also depends on the moisture content of the snow cover. From these physical fundamentals, the above-described snow parameters can be derived from information of propagation delays and signal strengths of microwave signals using mathematical and physical equations [10, 12, 15, 16].
    However, the determination of the snow parameters has never before been developed exclusively on the basis of the combination of the GNSS carrier phase with the GNSS signal strength measurements (raw data). The reason for this is that prior to the application of the present invention, the propagation delay of GNSS signals in a snowpack has never been developed based on GNSS carrier phase data. The present invention therefore relates to a method of measuring snow parameters according to claim 1. Preferred embodiments of the present invention are claimed in dependent claims 2 to 15.
    A corresponding apparatus for measuring microwave signals from navigation satellites (GNSS) is described and claimed in a co-pending patent application of the inventors of the present method invention entitled "Apparatus for Determining Snow Parameters". However, the method according to the invention is not limited to this device.
    Advantages of the Solution The advantages achieved with the invention are that on the one hand the snow parameters can be determined precisely with only two antennas A1, A2, which are connected to navigation signal receivers E1, E2. A further advantage is that the three snow parameters snow water equivalent, snow depth and snow light can all be determined with the same device, which was not possible before.
    The apparatus for determining snow parameters that can be used for the method according to the present invention is described and claimed in a co-pending patent application of the present inventors entitled "Apparatus for Determining Snow Parameters". However, the method according to the invention is not limited to this device.
    Another advantage of the inventive method is that it is a non-destructive measurement method: The snow cover is not affected by the measurement. In addition, freely available navigation satellite signals are usefully used in addition to their actually specific task of positioning and navigation. Consequently, it is a cost effective method. Since the navigation satellites are available worldwide and constantly, snow parameters can be continuously measured almost at any point on earth.
    The invention will be explained in more detail with reference to the three Figs. 1 to 3. The explanation, and in particular the reference to the figures are only illustrative and exemplary description of the invention, without the invention being limited thereto.
    In the figures: [0028]
    Fig. 1 is a schematic illustration of the spatial arrangement of the two GNSS antennas under (AI) and over (A2) a snow cover S on the bottom G, as it can be used by way of example for the determination of snow parameters. The direct distance B between the antennas is conventionally referred to as, baseline 11 (B). Fig. 1 also shows and the height H of the antenna A2 of the at least two antennas A1, A2 above the snow cover S above the ground G and the horizontal distance E of the two antennas A1 and A2 of the at least two antennas A1, A2 from each other, viewed parallel to Reason G; and
    2 is a flowchart of the process for determining the snow water equivalent (SWE), snow height (HS), and snow (LWC) snow parameters under dry (DS) (solid lines) and wet (WS) (dashed lines) snow conditions. The method is subdivided into an initialization phase (I), a decision phase (D), a measurement phase (M) with several steps of the processing and a result determination phase (R); and
    FIG. 3 shows, by way of example, the carrier phase residuals under no snow or dry snow conditions for different snow water equivalent values (SWE values) for a period of one day each. Here, a) includes a SWE value of 0 cm, i. no snow, b) a SWE value of 200 mm, c) a SWE value of 400 mm and d) a SWE value of 600 mm. The absolute value ranges of the carrier phase residuals r are proportional to the snow water equivalent (SWE).
    Detailed Description of the Claims / Technical Description of the Invention The present invention relates to a method for determining snow parameters of a snow cover S arranged on a base G. The term "snow parameters" is used in the context of the present description and in the claims in particular ( however, without limitation for the method according to the invention) the parameters snow water equivalent (SWE) of a snow cover S, snow depth (HS) of a snow cover S and snow cover (LWC) of a snow cover S understood.
    The method according to the invention for the determination of snow parameters is carried out in particular (but without restricting the method according to the invention) by means of a device which may comprise: at least two receivers E1, E2 of microwave signals from navigation satellites and at least two antennas A1, A2 which are connected to the at least two receivers E1, E2.
    The device which can be used in the method according to the invention is described and claimed in detail in the parallel patent application of the inventors entitled "Device for Determining Snow Parameters", which is incorporated into the present application by the reference with its full disclosure content. In this case, an antenna A1 of the at least two antennas A1, A2 is fixed on a base G under a snow cover S and another antenna A2 of the at least two antennas A1, A2 is fixed at a predetermined height H above the snow cover S in such a way that the two antennas A1, A2 of the at least two antennas A1, A2 have a defined distance E parallel to the base G and have a defined distance H perpendicular to the base G (see FIG. 1).
    The method according to the invention for determining snow parameters comprises four phases, which are carried out in each case at least one point in time (see FIG. 2): The first phase comprises an initialization or calibration phase (I), in which the relative positions (la) between the antennas (A1, A2) of the at least two antennas (A1, A2) are determined and reference measurements for the signal strength (Ib) are carried out: The antennas (A1, A2) receive microwave signals from navigation satellites (GNSS) and the connected receivers (E1, E2) determine pseudorange and carrier phase measurements from these microwave signals. The pseudorange and carrier phase measurements from the receiver E1 are subtracted from the corresponding measurements at the receiver E2 to produce differential pseudorange and carrier phase measurements. The differential pseudo-orange and carrier-phase measurements are linearly dependent on the relative position between the two antennas, so that the relative position can be determined by linear compensation calculation. When using the differential carrier phase measurements in addition to the relative position in addition, the ambiguities of the differential carrier phase measurements must be determined. Using the differential pseudo-orange measurements, optionally, the differential multipath errors of the differential pseudo-orange measurements can also be estimated to increase accuracy. The reference measurements for signal strength are carried out analogously to [15, 16] (Ib).
    In a second phase, which corresponds to a decision phase (D), it is decided whether there is a snowpack S on the ground G or does not exist. This decision is made on the basis of the differential carrier phase measurements, which are influenced by the snowpack S. The differential carrier phase measurements are also affected by the relative position between both antennas, which has already been determined in the initialization phase and can thus be corrected.
    In the decision phase, it is also decided whether the snow is wet or dry (Db). For this purpose one or more a priori known signal strength thresholds are used, e.g. <-3 dB after [15].
    In a subsequent third phase, which includes at least one measurement phase M, but may also include several measurement phases M immediately after one another or at arbitrary intervals, it is determined at least one time at which a snowpack S the reason G and the one Antenna AI of the at least two antennas (A1, A2) covered, the snow-related propagation delay in the zenith direction. For this purpose, differential carrier phase measurements are used, which are linearly dependent on the snow-related propagation delay. Thus, the snow-related propagation delay can be derived by linear compensation calculation from the differential carrier phase measurements. Since the differential carrier phase measurements are ambiguous and the differential ambiguities take on new values each time the receivers are turned off and on, they must also be determined. The measurement phase M therefore requires a determination of the snow-related propagation delay in the zenith direction as well as the ambiguities of the differential carrier phase measurements. The differential carrier phase measurements are also linearly dependent on the differential ambiguities so that a linear compensation calculation satisfies. However, the integerity of the ambiguities should be taken into account in order to achieve the highest possible accuracy.
    The individual sub-steps for deriving the snow-related propagation delay are described in detail below (preferred embodiments). In dry snow, these are the partial steps times to Mall; in wet snow, sub-steps Mb1 and Mb2 are additionally required.
    In a subsequent fourth phase is processed in the at least one measurement phase M at the two antennas A1, A2 of the at least two antennas A1, A2 measured and the connected receivers E1, E2 transmitted snow-time delay in the zenith direction and in In the case of wet snow, in addition, the signal strength measurement, which has been normalized to the reference measurement, which was carried out in the initialization phase I. The snow water equivalent (SWE) is determined as the result. The snow depth (HS) can be additionally calculated by adding a snow density information according to the previous version. In wet snow, the snow light (LWC) is additionally derived as a result of the decision determination phase R.
    The carrier phase measurements are determined on two GNSS receivers (E1, E2), with one GNSS antenna (A1, A2) on one pole above the snow and another receiver on the ground. The carrier phase measurements from both receivers (E1, E2) are subtracted to eliminate navigation satellite clock errors and atmospheric delays. The differential measurements thus obtained are referred to as "differential carrier phase measurements".
    The snow parameters are derived from the differential carrier phase measurements which, depending on the elevation and number of navigation satellites, can be measured to a precision of one millimeter to centimeter accuracy.
    Since the carrier signals are sinusoidal and thus periodic, the carrier phase measurements are ambiguous. The ambiguities of the carrier phase measurements are integer with respect to the wavelength. Therefore, not only the snow parameters but also the integer ambiguities of the differential carrier phase measurements have to be determined.
    These differential carrier phase measurements are strongly influenced by the clock errors of the two low-cost receivers. This influence can be eliminated by the selection of a reference navigation satellite and the difference between the differential carrier phase measurement of this reference navigation satellite and the differential carrier phase measurements of the other satellites. The reference navigation satellite is selected so that the elevation, signal strength and visibility are as large as possible. The thus obtained twice differentiated measurements are referred to below as double difference measurements.
    The double difference measurements are influenced by the following physical quantities: - relative position between both GNSS antennas - medium between both GNSS antennas (air, snow) - integer ambiguities of the double difference measurements of the carrier phase measurements The double difference measurements are temporal variable, where there are several reasons with different variability: - change in snow characteristics (significant in hours or longer) - change in navigation satellite elevations (significant in minutes or longer) - measurement noise (always present) - Insufficient synchronization of GNSS Receiver (significant in the period of microseconds or longer) In further preferred embodiments of the method according to the invention, which can be realized together with a feature of the invention or with several features of the invention or with all features of the invention, without the inventions As a result of the result determination phase (R) snow parameters of the snow cover S, the snow water equivalent (SWE), which describes the total water stored in liquid and solid form in the snowpack, is determined as the snow depth (HS) which determines the snow depth Height of the snowpack in the vertical direction to the bottom G describes, and the snowfall (LWC), which describes the percentage of liquid water in the snowpack are.
    In further preferred embodiments of the inventive method, which can be realized together with a feature of the invention or with several features of the invention or with all features of the invention, without limiting the invention thereto, in the case of dry snow (DS ) determine the snow water equivalent (SWE) as well as the snow depth (HS) and where, in the case of wet snow (WS), the snowfall (LWC) is also determined.
    In the case of dry snow, the snow propagation delay, as determined from the GNSS pseudorange and carrier phase measurements in the zenith direction, is compared to the assumed velocity of L-band microwave signals in dry snow, e.g. from [16] multiplied to obtain the snow water equivalent (SWE). With the addition of optional snow density information (eg from [13, 14]), snow depth (HS), snow snow equivalent (SWE) and snow density (SD) can be determined together with the calculated snow water equivalent (SWE) [12 ].
    In wet snow (WS), the calculation is more complex because in addition to the propagation delay in the zenith direction, derived from the GNSS pseudo orange and carrier phase measurements, the signal attenuation [10, 16], expressed as a reduction of C / N0 [15], must be considered by the occurrence of liquid water. In further preferred embodiments of the method according to the invention, which can be realized together with a feature of the invention or with several features of the invention or with all features of the invention, without limiting the invention thereto, WS is passed as a result of the result determination phase (R) under moist snow conditions the snow parameters snow water equivalent (SWE), snow depth (HS) and snowfall (LWC) together from the previously determined snow-related propagation delay and the normalized to the reference measurement
    Signal strength measurements with the optional addition of the density of snow, after which in the initialization phase (I) parallel to the determination of the relative position (la) of the two antennas (A1, A2) of the at least two antennas (A1, A2) a normalized reference (Ib) signal strength without snow cover (S) on the bottom (G). In the measuring phase (M) parallel to the processing of pseudorange and carrier phase measurements under snow conditions (Ma1-Ma11), the signal strength is processed under snow conditions, which determines dampening under wet snow conditions by the occurrence of liquid water in the snow cover S. From a marked GNSS signal strength reduction (<-3 dB, [15]), measured on the GNSS antenna on the bottom G, which is in the case of a snow cover S under the snow cover S, the snow is defined as wet. On the basis of the snow depth information and the signal strength measurement, it is also possible to calculate the liquid water content (LWC) according to [15, 16] using dielectric snow pattern models (for example [11]). The signal strength under snow conditions for each measured time step is related to the normalized reference (Mb1) [15, 16]. The normalized signal strength optionally linked to the dielectric properties of the snow, optionally using the assumption of a dry snow density and the propagation delay (of 1) (Mb2) (e.g., according to [16]).
    In further preferred embodiments of the inventive method, which can be realized together with a feature of the invention or with several features of the invention or with all features of the invention, without limiting the invention thereto, determined in the initialization phase (I) the Relative positions of the antennas (A1, A2) of the at least two antennas (A1, A2), the ambiguities of the differential carrier phase measurements and optionally the differential Mehrwegefehler together from the differential pseudorange and carrier phase measurements by linear compensation calculation (la).
    The determination of the snow parameters from double-differentiated carrier-phase measurements sets a general knowledge (accuracy in the range of a few meters) of the absolute position (for efficient calculation of the navigation satellite elevations) and a highly accurate knowledge of the relative position between the antennas A1 and A2 of the at least two antennas (to correct the double-differentiated carrier phase measurements) ahead. These positional data are determined in the initialization phase, i. at a time when there is no snow cover over the GNSS antenna A1 at the bottom.
    The three-dimensional relative position (baseline B) between the antennas A1 and A2 of the at least two antennas is determined from the double-differentiated pseudo orange and carrier phase measurements with any RTK method [1, 2, 7]. A central point of any RTK method is the exploitation of the integerity of the ambiguities of the differential carrier phase measurements. For low-cost GNSS receivers and GNSS antennas, the additional estimation of the pseudorange multipath errors in an extended RTK method is recommended. For more details on RTK positioning, see [3-6].
    In further preferred embodiments of the inventive method, which can be realized together with a feature of the invention or with several features of the invention or with all features of the invention, without limiting the invention thereto, determined in the measuring phase (M) the Elevation of the navigation satellites at the position of at least one of the antennas (A1, A2), and also the direction vectors between navigation satellites and at least one antenna (A1, A2) from the positions of the navigation satellites and the positions of at least one antenna (A1, A2) ( Times), and selects a satellite with the highest possible elevation, signal strength and long visibility as a reference satellite (Ma2).
    In further preferred embodiments of the inventive method, which can be realized together with a feature of the invention or with several features of the invention or with all features of the invention, without limiting the invention thereto, one additionally determines a synchronization correction (Ma3) for every differential carrier phase measurement.
    Since the clocks are not synchronized in inexpensive receivers and drift relatively strong, a synchronization correction for the double-differential measurements is required. This synchronization correction is derived from the movement of the navigation satellites within the time of the relative receiver clock error.
    In further preferred embodiments of the inventive method, which can be realized together with a feature of the invention or with several features of the invention or with all features of the invention, without limiting the invention thereto, formed in the measurement phase (M) doubly differentiated carrier phase measurements by subtracting the differential carrier phase measurements of the reference navigation satellite from the differential carrier phase measurements of all other navigation satellites; and, if necessary, additionally subtracting the synchronization correction and the double-differentiated distances between satellite and receiver, which are determined from the direction vectors between satellite and receiver and the relative position between the antennas (A1, A2) (Ma5); and optionally correcting, in addition, jumps in the double-difference carrier phase measurements (Ma6); and optionally additionally determining for each time step of a measurement the subset of the navigation satellites (Ma7) available, ascending and descending in the field of view of the antennas.
    In order to determine the snow parameters, the doubly differentiated measurements must first be corrected by some non-snow-specific parameters: These include firstly the synchronization correction and a geometry term. The latter includes the double-differentiated distances between satellite and receiver. Because the
    Distance between satellite and receiver is large compared to the distance between the two receivers, the direction vector between satellite and receiver may be assumed to be parallel for both receivers. Thus, the double-differentiated distance can be represented as a projection of the relative position between both GNSS antennas.
    In further preferred embodiments of the inventive method, which can be realized together with a feature of the invention or with several features of the invention or with all features of the invention, without limiting the invention thereto, one estimates in the measurement phase (M) initial (Ma8) the integer double-differentiated ambiguities of the double-differentiated carrier-phase measurements and the snow-related time delay in the zenith direction from a time series of double-differentiated carrier phase measurements by linear compensation calculation, wherein the projection of the snow-related propagation delay from the direction of incidence on the Zenit direction using the known elevations of the navigation satellites used.
    The corrected double-differentiated carrier phase measurements are dependent on the differential propagation delay in the snow and the double-differentiated ambiguities of the carrier phase measurements. The propagation delay in the snow, in turn, depends on the elevation of the navigation satellites and the snow depth. Since the elevation of the navigation satellites can be assumed to be known a priori, the propagation delays of the double-dif ference carrier phase measurements of all navigation satellites can be represented as a function of a single (i.e., scalar) delay in the zenith direction. Thus, K ambiguities and 1 propagation delay in the zenith direction have to be determined from the K double-differentiated carrier-phase measurements. Since the number of unknowns exceeds the number of measurements by one, measurements of several times are required. The separability between the temporally constant carrier phase ambiguities and the snow-related propagation delays is made possible by the change in satellite geometry. The duration of an overflight of a navigation satellite is usually up to 6 hours, so that the satellite geometry changes only slowly and measurements of a longer period of several hours are required.
    The integerity of the ambiguities is initially neglected, i. a real-valued estimate of the ambiguities and snow parameters is derived from the double-differentiated carrier phase measurements. For this purpose, a linear compensation calculation is applied which minimizes the quadratic deviation between measured and calculated double-differentiated measurements. The conditioning of the equation system can be significantly improved by using a rough a priori information of the propagation delay in the snow. This can be derived, for example, from the snow parameters of the previous day. In a second step, the real-valued estimates of the ambiguities are mapped to integer values. For this, a simple rounding, a sequential rounding or a systematic search can be used. The real-valued ambiguity estimates are highly correlated so that sequential rounding and systematic searching yield better results than simple rounding. The reliability of the ambiguity information can be significantly increased by the integration of a priori information about the snow-related propagation delay in the zenith direction in the ambiguity search. For this, only that ambiguity solution is used that leads to consistent snow parameters.
    In further preferred embodiments of the inventive method, which can be realized together with a feature of the invention or with several features of the invention or with all features of the invention, without limiting the invention thereto, one additionally determines in the measurement phase (M) (Ma9) the integer double-differentiated ambiguities of the carrier phase measurements of the newly-launched navigation satellites from the difference rounded to the nearest integer between the double-differentiated carrier phase measurements and the double-differentiated calculated carrier phase measurements, the double-differentiated calculated carrier phases Measurements from the product between the projection of the snow-related propagation delay from the direction of incidence to the zenith direction can be determined by means of the known elevations of the navigation satellites and the snow-related propagation delay in the zenith direction.
    The satellite geometry changes continuously due to the Earth's rotation and the orbiting navigation satellites, so that within a measurement cycle individual navigation satellites rise or fall above the horizon or local elevations. The former requires an initialization of the ambiguities of the newly-emerging navigation satellites. The ambiguities are determined by linear compensation calculation based on the elevation of the newly-rising navigation satellites and the zenith-time propagation delay known from the other navigation satellites.
    In further preferred embodiments of the method according to the invention, which can be realized together with a feature of the invention or with several features of the invention or with all features of the invention, without limiting the invention thereto, residues (M) are formed in the measurement phase the double-differential carrier phase measurements by subtracting the double-differentiated carrier-phase ambiguities from the double-differential carrier-phase measurements, and determining the snow-related propagation delay in the zenith direction from the residuals of the double-differentiated carrier-phase measurements by linear compensation calculation, wherein the projection of the snow-related propagation delay from the direction of incidence to the zenith direction is formed and used by means of the known elevations of the navigation satellites (Ma10).
    Once the ambiguities are fixed to integer values, they are subtracted from the corrected double-differentiated carrier phase measurements. The residuals of the fixed double-differentiated carrier phase measurements thus obtained depend only on the snow-related propagation delay in the zenith direction. This propagation delay in the zenith direction is determined by linear compensation calculation from the residuals of the fixed and corrected double-differentiated carrier phase measurements. The residuals are directly proportional to the snow water equivalent (SWE). The snow water equivalent (SWE) can therefore be determined from the residuals of all navigation satellites by means of linear compensation calculation on the basis of the signal propagation speed and the known satellite geometry.
    In Fig. 3 this is exemplified for continuous GNSS measurements on four days, in which the SWE values have been set between 0 and 600 mm. This also reflects the previously described variability of the double-differentiated carrier phase measurements, in particular with regard to the influence of the snow. The arch-like courses of the residuals are due to the changes in the elevations of the navigation satellites, which lead to different maturities in the snow.
    In further preferred embodiments of the inventive method, which can be realized together with a feature of the invention or with several features of the invention or with all features of the invention, without limiting the invention thereto, reviewed and optionally corrects the double-differentiated Ambiguities as soon as the elevation of a navigation satellite near the elevation of the reference navigation satellite is determined by means of the double-differentiated carrier phase measurements (Ma11) normalized to the wavelength and then rounded to the nearest integer.
    A correct estimation of the ambiguities is a prerequisite for a precise determination of the snow parameters. Therefore, a plausibility check is performed for the ambiguity estimation. This checks the residuals of the fixed double-differentiated carrier phase measurements as soon as the elevation of a navigation satellite is close to the elevation of the reference navigation satellite. At this time, the snow related propagation delays for the selected navigation satellite correspond to the propagation delay of the reference navigation satellite such that the differential snow related propagation delay is close to zero and thus the residuals of the fixed dual-differential carrier phase measurements would also have to be close to zero. If not, the ambiguity estimate is adjusted accordingly.
    In further preferred embodiments of the inventive method, which can be realized together with a feature of the invention or with several features of the invention or with all features of the invention without limiting the invention thereto, increasing the accuracy of the particular snow-related propagation delay in Zenith direction by averaging or filtering the particular snow-related propagation delay over time. The filtering may be, for example, a simple averaging or a low-pass filter.
    In further preferred embodiments of the method according to the invention, which can be realized together with a feature of the invention or with several features of the invention or with all features of the invention, without limiting the invention thereto, wherein the antenna installed above the snow cover (FIG. A2) and the receiver (E2) are replaced by a virtual reference station, the virtual reference station deriving pseudo-orange, carrier phase and signal strength measurements by linear combination of pseudorange, carrier phase and signal strength measurements from a network of reference stations.
    The inventive method has been described in detail above with reference to the figures, which relate to preferred embodiments of the method. However, the invention is not limited to the preferred embodiments shown in the figures and described in the description. Rather, the scope of the invention is determined by the following claims.
    REFERENCE NUMBERS: A1 antenna on the ground G under the snow cover S A2 antenna above the snow cover SG base S snow cover DS dry snow conditions WS wet snow conditions B base line H height (vertical distance) of the one antenna (A2) above the snow cover S above the reason G is positioned
    E distance E of the two antennas (A1, A2) of the at least two antennas (A1, A2) parallel to the base G
    权利要求:
    Claims (12)
    [1]
    I Initialization phase D Decision phase M Measurement phase R Result determination phase r Carrier phase residuals Time Patent claims
    1. A method for determining snow parameters of arranged on a base G snow cover S with at least two receivers (E1, E2) of microwave signals from navigation satellites, each with an antenna (A1, A2) are connected, wherein an antenna (AI) of at least two antennas (A1, A2) are fixed on the bottom G under a layer of snow S and another antenna (A2) of the at least two antennas (A1, A2) is fixed above the layer of snow S; comprising the four phases, that a) in an initialization phase (I) without snow cover S on the bottom G and with at least one antenna (A1) of the at least two antennas (A1, A2) the relative positions between the antennas (A1, A2 ) are determined by means of received microwave signals from navigation satellites, wherein the receivers (E1, E2) derive pseudorange and carrier phase measurements from the received microwave signals, from which differentiated pseudorange and carrier phase measurements are determined by difference between the measurements of both receivers, and the relative Positions from the differential pseudo-orange measurements and carrier phase measurements can be determined by linear compensation calculation (la); and performs parallel reference measurements on signal strength (Ib); b) in a decision phase (D) at least one time at which a snow cover S covers the base G and the one antenna A1 of the at least two antennas (A1, A2), first by means of carrier phase measurements the presence of a snow cover (Da) and Subsequently, by means of the signal strength, the occurrence of snow moisture (Db) of the then received microwave signals from navigation satellites determines whether the snow is dry or moist; c) in at least one measurement phase (M) at least one time at which a snow cover S covers the base G and the one antenna A1 of the at least two antennas (A1, A2), the snow-related propagation delay in the zenith direction and the ambiguities of the differential Determine carrier phase measurements by means of the differential pseudorange measurements and carrier phase measurements derived from the then received microwave signals from navigation satellites; and parallel measurements of signal strength are performed; d) determines at least one snow parameter from the snow-related propagation delay determined in the measurement phase (M) in at least one result determination phase (R); and, if appropriate, further properties of the snow in the determination of the snow parameters of the snow cover S arranged on the bottom G in the measuring phase (M) and result determination phase (R).
    [2]
    2. The method for determining snow parameters according to claim 1, wherein the snow parameter determined in result determination phase (R) describes the snow water equivalent (SWE) describing all the water stored in liquid and solid form in the snowpack in vertical direction, the snow depth (HS ), which describes the height of the snowpack in the vertical direction above the ground G, and the snowfall light (LWC), which describes the percentage of liquid water in the snowpack, are,
    [3]
    3. A method for determining snow parameters according to claim 1 to 2, wherein in the case of dry snow (DS) the snow water equivalent (SWE) and optionally adding the snow density (SD) determines the snow depth (HS) and wherein in the case of wet Snow (WS) also derives the snow light (LWC) together from the previously determined snow-related propagation delay in the zenith direction and the normalized to the reference measurement signal strength measurements.
    [4]
    4. Method for determining snow parameters according to one or more of claims 1 to 3, wherein in the initialization phase (I) the relative positions of the antennas (A1, A2) of the at least two antennas (A1, A2), the ambiguities of the differential carrier phases Measurements and, optionally, the differential multipath errors jointly determined from the differential pseudorange and carrier phase measurements by linear compensation calculation (1a). 5. A method for determining snow parameters according to one or more of claims 1 to 3, wherein in the measuring phase (M) the elevation of the navigation satellites at the position of at least one of the antennas (A1, A2) and the direction vectors between navigation satellites and at least one antenna (A1, A2) from the positions of the navigation satellites and the positions of at least one antenna (A1, A2) determined (times), and a navigation satellite with the highest possible elevation, signal strength and long visibility as a reference satellite (Ma2) selects.
    [6]
    6. A method for determining snow parameters according to one or more of claims 1 to 5, wherein additionally a synchronization correction for each differential carrier phase measurement is determined (Ma3).
    [7]
    7. A method for determining snow parameters according to one or more of claims 1 to 6, wherein in the measuring phase (M) double-differentiated carrier phase measurements by subtracting the differential carrier phase measurements of the reference navigation satellite from the differential carrier phase measurements of all other navigation satellites (Ma4); and, if necessary, additionally subtracting the synchronization correction and the double-differentiated distances between satellite and receiver, which are determined from the direction vectors between satellite and receiver and the relative position between the antennas (A1, A2) (Ma5); and possibly additionally correcting jumps of the double-differentiated carrier-phase measurements (Ma6); and optionally additionally determining for each time step of a measurement the subset of the navigation satellites (Ma7) available, ascending and descending in the field of view of the antennas.
    [8]
    8. A method for determining snow parameters according to one or more of claims 1 to 7, wherein in the measurement phase (M) initial (Ma8) the integer double-differentiated ambiguities of the carrier phase measurements and the snow-related propagation delay in the zenith direction from a time series of doubly differentiated Carrier phase measurements determined by linear compensation calculation, wherein one forms the projection of the snow-related propagation delay from the direction of incidence to the zenith direction by means of the known elevations of the navigation satellites.
    [9]
    9. A method for determining snow parameters according to one or more of claims 1 to 7, wherein in the measurement phase (M) in addition (Ma9) the integer double-differentiated ambiguities of the carrier phase measurements of the new rising satellites from the navigation to the nearest Number of rounded difference between the double-differentiated carrier phase measurements and the double-differentiated calculated carrier phase measurements determined, with the double-differentiated calculated carrier phase measurements from the product between the projection of the snow-related propagation delay from the direction of incidence to the zenith direction by means of known elevations of the navigation satellites and the snow-related propagation delay in the zenith direction.
    [10]
    10. A method for determining snow parameters according to one or more of claims 1 to 9, wherein in the measuring phase (M) residuals of the double-differentiated carrier phase measurement by subtraction of the double-differentiated carrier phase ambiguities of the double-differentiated carrier phase measurements is formed, and wherein the snow-related propagation delay in the zenith direction by linear compensation calculation of the residuals of the double-differentiated carrier phase measurements, wherein the projection of snow-related propagation delay from the direction of incidence to the zenith direction by means of the known elevations of the navigation satellites forms and used (Ma10).
    [11]
    11. A method for determining snow parameters according to one or more of claims 1 to 10, wherein the derived double-differentiated ambiguities of at least one double-differentiated carrier phase measurement are checked and, if necessary, the double-differentiated ambiguities are corrected as soon as the elevation of a navigation satellite is approaching The elevation of the reference navigation satellite is determined by means of the double-differentiated carrier phase measurements (Ma11) which are normalized to the wavelength and then rounded to the nearest whole number.
    [12]
    12. A method for determining snow parameters according to one or more of claims 1 to 11, wherein increasing the accuracy of the particular propagation delay in the zenith direction by an averaging or filtering.
    [13]
    13. A method for determining snow parameters according to claim 1, wherein the over-the-snow antenna A2 and the receiver (E2) are replaced by a virtual reference station, the virtual reference station detecting pseudorange, carrier phase and signal strength measurements from the pseudorange, Derive carrier phase and signal strength measurements from a network of reference stations.
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    同族专利:
    公开号 | 公开日
    DE102017110994A1|2017-12-28|
    DE102017110992A1|2017-12-28|
    CH712623B1|2022-01-31|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US11092716B1|2018-01-22|2021-08-17|NWB Sensors, Inc|Method of determining snowpack parameters using global navigation satellite system receivers|EP2749900A1|2012-12-28|2014-07-02|Amconav GmbH|Method for determining a baseline between two receivers|WO2020087787A1|2018-11-02|2020-05-07|北京讯腾智慧科技股份有限公司|Snow layer thickness monitoring method and system employing beidou system and multiple sensors|
    法律状态:
    2020-07-15| PCOW| Change of address of patent owner(s)|Free format text: NEW ADDRESS: GOTTHARDSTRASSE 40, 80686 MUENCHEN (DE) |
    优先权:
    申请号 | 申请日 | 专利标题
    DE102016007718|2016-06-23|
    DE102017110994.3A|DE102017110994A1|2016-06-23|2017-05-19|Method for the determination of snow parameters|
    DE102017110992.7A|DE102017110992A1|2016-06-23|2017-05-19|Device for the determination of snow parameters|
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