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.
Highlights
Surface soil moisture is one of the most significant quantities in the hydrological cycle [1]
We evaluated the Soil Moisture and Ocean Salinity (SMOS) Level 1C Brightness Temperature (TBSMOS) and Level 2 Soil Moisture (SMSMOS) from SMOS MIR_SCLF1C and SMOS MIR_SMUDP2 products, respectively
We developed two algorithms based on the L-MEB model to validate TBSMOS and SMSMOS data
Summary
Surface soil moisture is one of the most significant quantities in the hydrological cycle [1]. Direct measurements of ground-based soil moisture are only available at point scale, and measuring this parameter at large scales is significantly costly, time-consuming and, sparse in most regions. These measurements are not practicable for long periods and over wide areas [10]. The Advanced Scatterometer (ASCAT) is a C-band (5.255 GHz) active microwave remote sensing instrument onboard the Meteorological Operational (METOP) satellite series to provide global soil moisture data sets with a spatial resolution of 25 or 50 km [18]. Sentinel-1 mission provides SAR data at C-band that can be used to retrieve and map temporal changes of soil moisture underneath vegetation cover [12,19,20]
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