Abstract
Global navigation satellite system reflectometry technology (GNSS-R) is rarely used for river flow velocity inversion, and in particular, there is currently no research using the BeiDou Navigation Satellite System reflectometry technology (BDS-R) for river flow velocity inversion. In this paper, a carrier phase observation of river flow velocity inversion model is proposed. The interference phase is the integral of the Doppler frequency. The raw intermediate frequency (IF) data sets are processed through an open-loop method to obtain the Doppler frequency observation generated by river flow and then realize velocity inversion. The shore-based river current measurement was conducted on the south bank of Dashengguan Yangtze River in Nanjing city, Jiangsu Province, for nearly two hours on 22 April 2021. After realizing the inversion of river flow velocity in GPS L1, the combined inversion of BDS B1I GEO satellite and IGSO satellite is realized for the first time, which demonstrates the feasibility of river flow velocity inversion using BDS reflected signals. Compared with the real river flow velocity, the GPS L1 PRN 4 (1st period) inversion precision reaches up to 0.028 m/s (mean absolute error, MAE) and 0.036 m/s (root mean square error, RMSE). In parallel, BDS GEO 2 inversion precision can reach 0.048 m/s (MAE) and 0.063 m/s (RMSE), and BDS IGSO 10 inversion precision is 0.061 m/s (MAE) and 0.073 m/s (RMSE). These results illustrate that satellite elevation change rate and distance between specular points and current meter may have a negative effect on the accuracy of river flow velocity inversion. Specular points obstructed by obstacles or too far from the velocity meter may introduce uncertain error in both MAE and RMSE. Neither the satellite elevation nor the signal strength has an obvious correlation with inversion precision, which is consistent with the theoretical principle.
Highlights
River flow velocity detection is of great significance in hydrology work
When GNSS satellite signals are reflected by the river in the target region, the Doppler frequency shift caused by the river flow velocity is the low-frequency component in the spectrum, due to the very low river flow compared with the satellite’s velocity
The hardware used in the experiment was a miniature Global navigation satellite system reflectometry technology (GNSS-R) detector designed and manufactured by Shanghai Aerospace Electronics Institute, which is made of a left-hand circular polarization antenna (LHCP), right-hand circular polarization antenna (RHCP), and hardware delay/Doppler-mapping receiver (DDMR)
Summary
River flow velocity detection is of great significance in hydrology work. It is an essential fundamental link in hydrologic detection, hydrologic prediction, hydrodynamic research, flood control engineering design, and ecological environment assessment [1]. 2022, 14, 1170 sea ice sensing [10–12], inland water detection [13,14], sea surface oil slicks [15,16], sea surface effective wave height [17,18], and other application fields Better yet, it still has great potential in the applications of remote sensing inversion. In 2015, Weihua Bai et al published a new potential application of GNSS-R through carrier phase observation [30], inversion of river flow velocity, and verified its feasibility by using GPS. The GEO satellites have low angular velocity and almost no change in elevation Their maximum speed is between 80 m/s and. The combination of B1I GEO satellite and IGSO satellite of BDS is used to carry out river flow velocity inversion for the first time. The velocity inversion results are compared with the actual velocity, and the influence of satellite elevation angle change rate and satellite signal intensity on the accuracy of river flow velocity inversion is further explored
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