Abstract
When the interferometric global navigation satellite system reflectometry (iGNSS-R) altimeter receives the direct and reflected signals through the digital multibeam phased array antenna, the roll-off of element radiation pattern will cause the scanning loss of directivity. If the scanning loss is neglected, the ocean altimetric precision will be biased with possible consequences for the instrument design. This article carries out the following research on this. First, based on the geometry of iGNSS-R altimetry and the principle of phased array antenna beamformer, the scanning loss model with the elevation angle at the specular point as a parameter is established. Second, this article uses the measured data of the phased array antenna to verify the model, and the result shows that the simulated value is in good agreement with the measured value, with an average deviation of 0.07 dB. Third, taking the GPS L1 signal (full composite) as an example, the model is used to analyze the influence of the scanning loss on the iGNSS-R altimetric precision estimation. The research results show that when the phased array antenna synthesizes four beams for iGNSS-R altimetry, the comprehensive effect of scanning loss on altimetric precision estimation is 0.16 m. The influence of scanning loss should be considered in the future high-precision iGNSS-R altimetry instrument design.
Highlights
T HE global navigation satellite system reflectometry (GNSS-R) ocean altimetry is an innovative and powerful earth observation technology integrating satellite navigation and Manuscript received August 14, 2020; revised October 30, 2020, November 30, 2020, and December 16, 2020; accepted December 16, 2020
We proposed the nadir antenna observation capability optimization method to increase the number of sea surface reflected signals received by conventional GNSS-R (cGNSS-R) satellite [18]
This section obtains the scanning loss at different elevation angles according to the scanning loss model, and analyzes the influence of the scanning loss on the signal-to-noise ratio (SNR) and precision estimation of the interferometric global navigation satellite system reflectometry (iGNSS-R) ocean altimetry
Summary
T HE global navigation satellite system reflectometry (GNSS-R) ocean altimetry is an innovative and powerful earth observation technology integrating satellite navigation and Manuscript received August 14, 2020; revised October 30, 2020, November 30, 2020, and December 16, 2020; accepted December 16, 2020. We proposed the nadir antenna observation capability optimization method to increase the number of sea surface reflected signals received by cGNSS-R satellite [18] These spaceborne GNSS-R missions are mainly used for wind speed retrieval rather than ocean altimetry. The error of using the TDS-1 and the CYGNSS observations to retrieve SSH is above 2.5 m (1 Hz) [7], [8], which is because the directional antennas with low directivity (less than 15 dB), resulting in low signal-to-noise ratio (SNR) of the received signal, and the bandwidth of the C/A code (2.046 MHz) is relatively narrow [19] These two factors limit the performance of cGNSS-R ocean altimetry. Taking TDS-1 as an example, the model is used to comprehensively evaluate the influence of scanning loss on altimetric precision estimation
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