SYSTEM AND METHOD FOR MEASURING RAINFALL RATE FROM THE ANALYSIS OF GNSS SIGNALS AND HYDROLOGICAL STATION EQUIPPED WITH SUCH A SYSTEM

Abstract

The technical field of the invention is that of systems and methods for measuring rainfall rates. The invention also relates to a hydrological monitoring station equipped with such a rain rate measuring system.

Description

Title of the invention: SYSTEM AND METHOD FOR MEASURING THE RAIN RATE FROM THE ANALYSIS OF GNSS SIGNALS AND HYDROLOGICAL STATION EQUIPPED WITH SUCH A SYSTEM Technical field of the invention

[0001] The technical field of the invention is that of systems and methods for measuring rainfall rate. The invention also relates to a hydrological monitoring station equipped with such a rain rate measuring system. Technological background

[0002] The system targeted by the invention is referred to throughout the text as the RainGNSS system. This system aims to use the GNSS space constellation to locally improve rainfall rate measurements at the territorial scale, and thus supplement the existing data networks which are too few in number to predict extreme events such as flooding.

[0003] The system has multiple objectives: to improve knowledge and forecasting of flood phenomena on the one hand, to participate in more precise satellite measurement of the height of watercourses and hydrological reservoirs on the other hand, and to densify a meteorological monitoring system for water vapour and precipitation, which is critical in monitoring extreme events.

[0004] Indeed, among the impacts of climate change, it is established that territories will have to manage in the future more numerous and more intense rain events, while at the same time facing a water shortage, with strong economic consequences on agriculture in particular.

[0005] In view of this observation, the RainGNSS system complements the hydrology service offer provided by the micro-station proposed by the applicant in application WO2023174922 by measuring at the same location meteorological information on precipitation and humidity in the atmosphere (water vapor and rain). The combination of the use of a low-cost GNSS chip and associated algorithmic processing are the main object of this invention.

[0006] Distributed over watercourses, the applicant's network of micro-stations described in the aforementioned patent document provides continuous and high-frequency measurement of various hydrological parameters (height, velocity, turbidity) with excellent accuracy. This system therefore addresses the lack of data and the need growing need for river monitoring for a wide range of applications in the context of current climate change.

[0007] In order to better predict floods and in particular so-called "flash" floods, it is crucial to have a simultaneous measurement of precipitation observations in addition to the level of watercourses. The aim is to predict the arrival and amplitude of the flood wave using meteorological precipitation forecasts. This historicity is not achievable without in-situ equipment co-located at the water height and flow measurement stations (the depositor's micro-stations), and the observations provided by the weather or rain radars are generally provided at insufficient spatial resolution when we are interested in small hydrological basins, as demonstrated by the recent floods on the Vésubie and the Roya in October 2020.The integration of a GNSS sensor into the micro-station and the development of algorithms determining the precipitation rate from the measurements provided by this sensor are the subject of this invention which is an important advance for flood prevention.

[0008] On the other hand, the application of space measurements to the monitoring of the height of lakes and rivers is a rapidly expanding field, particularly with the upcoming arrival of data from the SWOT mission. The integration of a coincident measurement of the height of water and humidity in the atmosphere, including a rainfall rate, within a network of in-situ measurements will allow a more precise validation of these data and therefore the improvement of their accuracy.

[0009] The impact of disturbances on the GNSS signal and the estimation of water vapor from data from GNSS receivers designed for this use is a well-understood field. This vapor product is already used for the validation of satellite data. However, heavy rain also disrupts the GNSS signal, demonstrating the possibility of extracting a rain rate from it. Statement of the invention

[0010] The principle of the RainGNSS system is to use a dual-frequency, multi-constellation receiver on board a hydrological micro-station and to position the adapted receiving antenna above the station with a clear 360° view of the sky.

[0011] The principle consists of carrying out the precise positioning of the antenna using PPP (Precise Point Positioning) processing using the open source software RTKLIB. This GNSS positioning software makes it possible to calculate the precise positioning ( <lcm) de l’antenne et de suivre son évolution au cours du temps, le système GNSS réalisant des mesures toutes les minutes durant toute la vie de la micro-station. Lors de ce positionnement, le retard de l’onde GNSS (onde électromagnétique émise dans les bandes Ll, L2, L5 et L7 par les constellations GPS, GLONASS et GALILEO) due to tropospheric effects is estimated at the zenith of the antenna. This is called ZTD (Zenith Total Delay).

[0012] Indeed, the troposphere is the lower part of the atmosphere (approximately below 12 km). Radio signals transmitted by GNSS satellites are attenuated and delayed by the refractivity of the neutral atmosphere up to 60 km due to the Fermât principle, and this delay must be taken into account in GNSS positioning. The tropospheric effect is theoretically divided into two parts: dry and wet, and the total delays on the tropospheric path are therefore divided accordingly. While the dry component (reaching up to 2.3 m at the zenith) can be sufficiently modeled using atmospheric pressure, the wet component (reaching up to 50 cm at the zenith) depends on a large spatio-temporal variability of temperature and humidity. Therefore, it is often modeled in the estimation procedure as an additional time-varying unknown parameter.To avoid an over-parameterized system, a parameter (ZTD, the total zenith delay projected in the line-of-sight directions using a matching function) is estimated for a single station and a given time interval (or using a stochastic process).

[0013] Thus once the ZTD is calculated, the dry component is removed using models well known in the literature. The resulting wet part combines the effects of 2 components, water vapor and precipitation. The principle of RainGNSS is to estimate the precipitating part via a physical or empirical algorithm (statistics, machine learning, etc.) taking as input the ZTD without the dry component and collocating the rainfall data via measurements and models.

[0014] Once this restitution model has been created, the precipitation can then be estimated using only the ZTD estimates coming from the RTKLIB software running on the GNSS measurements from the micro-station, after having removed the dry component from the models.

[0015] This principle of estimating the rain rate by analyzing GNSS signals is advantageously integrated into a new hydrological micro-station proposed by the applicant.

[0016] The hydrological micro-station described in patent document WO2023174922 is an instrument dedicated to measuring the height of the water surface and the surface velocity of hydrological systems by remote sensing. Fully autonomous, the 850 nm LiDAR is combined with a nadir camera and a 3G / 4G mobile chipset, the whole being energy autonomous from a battery / solar panel pair. Embedding a specific LiDAR, the height measurements are carried out by the integration of a set of pulses guaranteeing centimeter precision. The LiDAR and camera combination allows intelligent post-processing of the measurements in order to provide reliable information for monitoring hydrological systems and warning during flood or drought episodes.

[0017] Due to its size and weight, the micro-station blends into the environment in which it plays its role as sentinel. Only the solar panel remains visible after installation.

[0018] This micro-station simply needs to be positioned above the hydrological contexts, fixed using a simple fastener (simple screw or even magnet if the structure receiving the micro-station is metallic). The solar panel is also fixed using the same simple system. 30 minutes are enough for installation and commissioning. Without contact with water, the micro-station requires reduced maintenance. Its durability and measurement stability are therefore superior to those of submerged sensors.

[0019] Currently equipped with 3G / 4G connectivity, the micro-station automatically sends its data in real time and at regular intervals. When the water level exceeds a threshold defined by the user, the micro-station automatically increases its acquisition frequency for a possible real-time alert. The micro-station also transmits all of its vital parameters by telemetry, thus allowing its remote monitoring and updating.

[0020] The new version of the micro-station allowing the RainGNSS system to be embedded, the subject of this patent, brings several new features compared to the previous version.

[0021] First of all, a completely new motherboard was developed to improve the robustness of the station to an industrial level.

[0022] Then, a wide-angle and infrared camera is used instead of the previous camera. An infrared LED projector positioned around the camera allows for night vision of the monitored scene.

[0023] An accelerometer was added in order to be able to control the attitude of the micro-station in real time.

[0024] An external GSM antenna has been added to optimize reception.

[0025] Preparation for receiving the future Kinéis chip to ensure connectivity via spatial IoT in white zones or in the event of a GSM connectivity failure has been added. This preparation allows the Kinéis chip to be installed as soon as the service is operational in 2024.

[0026] A temperature sensor has been added to measure the water surface temperature.

[0027] Finally, a dual-frequency, tri-constellation GNSS receiver and a GNSS antenna were added in order to be able to precisely position the micro-station in space, to monitor its positioning and finally to enable the development of the RainGNSS system for precipitation measurement.

[0028] The table below lists the main technical characteristics of the new version of the microstation.

Claims

Claims

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