River Slope Observation From Spaceborne GNSS-R Carrier Phase Measurements: A Case Study

This letter demonstrates the potential of estimating river surface slope using space-borne global navigation satellite system-reflectometry (GNSS-R) carrier phase measurements. A case study is presented where the slopes of several segments of the Orinoco river are retrieved based on the processing of raw intermediate-frequency (IF) data recorded by the cyclone global navigation satellite system (CYGNSS) mission. The retrieved river slopes mostly vary between 3.9 and 5.1 cm/km and are in agreement with the surveyed mean slope of 4.5 cm/km for the lower Orinoco River. The correction and calibration of several systematic errors, i.e., CYGNSS satellite orbit errors, tropospheric and ionospheric effects, and river surface reference height error, are discussed in this letter. For the Orinoco River case study, the river slope retrieval is calibrated using the reflection signal over a nearby lake to mitigate the mis-modeled and unmodeled errors. Analysis of the specular point (SP) tracks of GPS reflection signal indicates that CYGNSS has the potential to provide river slope observations for rivers that have sufficient width with high temporal and spatial resolutions.