Quantifying the effect of salinity on dielectric-based soil moisture measurements using COSMOS records

•COSMOS is an effective method for SM estimation in coastal salinized areas.•COSMOS is used to quantify the effect of soil salinity on multi-scale SM data.•SM sensors can be evaluated by COSMOS in saline soil and further calibrated.•L-band is more disturbed by soil salinity than C-band for satellite-based SM. Accurate Soil Moisture (SM) measurements are essential for agronomic practices and environmental applications in coastal saline areas. However, soil salinity can introduce significant errors in state-of-the-art SM measurements based on dielectric theory. The Cosmic-ray Soil Moisture Observing System (COSMOS) has the advantage of measuring SM independent of soil salinity, with a field-scale resolution between the point scale and the coarse scale. This paper utilizes COSMOS records to assess the effect of salinity on three types of SM sensors (HydraProbe, CS655, and 5TE) and five mainstream satellite-based SM products (AMSR-2, ACSAT, SMOS, SMAP, and CYGNSS). The experimental site is located in a typical coastal saline area of the Yellow River Delta, China. The findings and conclusions mainly include: 1) all three types of SM sensors are affected by the soil salinity, the HydraProbe outperforms CS655 and 5TE when compared to COSMOS SM, and the accuracy of HydraProbe and CS655 could be improved based on a proper calibration method, 2) L-band SM products are more disturbed by soil salinity than C-band, with mean ubRMSE=0.102 m3 m−3 for L-band vs. mean ubRMSE=0.068 m3 m−3 for C-band, and 3) COSMOS has the potential to bridge the knowledge gap in multi-scale dielectric-based SM from point scale to coarse scale.