Validation of the SMOS Level 1C Brightness Temperature and Level 2 Soil Moisture Data over the West and Southwest of Iran

Abstract

The European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) mission with the MIRAS (Microwave Imaging Radiometer using Aperture Synthesis) L-band radiometer provides global soil moisture (SM) data. SM data and products from remote sensing are relatively new, but they are providing significant observations for weather forecasting, water resources management, agriculture, land surface, and climate models assessment, etc. However, the accuracy of satellite measurements is still subject to error from the retrieval algorithms and vegetation cover. Therefore, the validation of satellite measurements is crucial to understand the quality of retrieval products. The objectives of this study, precisely framed within this mission, are (i) validation of the SMOS Level 1C Brightness Temperature (TBSMOS) products in comparison with simulated products from the L-MEB model (TBL-MEB) and (ii) validation of the SMOS Level 2 SM (SMSMOS) products against ground-based measurements at 10 significant Iranian agrometeorological stations. The validations were performed for the period of January 2012 to May 2015 over the Southwest and West of Iran. The results of the validation analysis showed an RMSE ranging between 9 to 13 K and a strong correlation (R = 0.61–0.84) between TBSMOS and TBL-MEB at all stations. The bias values (0.1 to 7.5 K) showed a slight overestimation for TBSMOS at most of the stations. The results of SMSMOS validation indicated a high agreement (RMSE = 0.046–0.079 m3 m−3 and R = 0.65–0.84) between the satellite SM and in situ measurements over all the stations. The findings of this research indicated that SMSMOS shows high accuracy and agreement with in situ measurements which validate its potential. Due to the limitation of SM measurements in Iran, the SMOS products can be used in different scientific and practical applications at different Iranian study areas.

A Novel Method for Long Time Series Passive Microwave Soil Moisture Downscaling over Central Tibet Plateau

“…Based on the observed data of microwave remote sensing, microwave SSM products with varied spatial coverage, varied time coverage, and varied accuracy have been retrieved and released. The widely used global products are as follows: the Soil Moisture Active Passive (SMAP, 3 km, 9 km and 36 km) [9,10] and the Advanced Microwave Scanning Radiometer-Earth Observing System sensor (AMSR-E) datasets (25 km) released by the National Aeronautics and Space Administration (NASA) [11,12], the Soil Moisture and Ocean Salinity (SMOS, 25 km) [13,14] and the Climate Change Initiative (CCI, 0.25 • ) datasets released by the European Space Agency [3,15], the Advanced Microwave Scanning Radiometer 2 (AMSR2, 0.25 • ) dataset released by the Japan Aerospace Exploration Agency (JAXA) [16], and the FengYun-3 dataset (25 km) released by the China Meteorological Administration [17,18]. The revisit interval of the above satellites/sensors is 1-3 days.…”