Comparison and Downscale of AMSR2 Soil Moisture Products with In Situ Measurements from the SCAN–NRCS Network over Puerto Rico

Jonathan Nuñez-Olivieri,Andmorgan Fisher,Tarendra Lakhankar,Rebecca Tirado-Corbalá,Jonathan Muñoz-Barreto

doi:10.3390/hydrology4040046

Abstract

A continuous spatio-temporal database of accurate soil moisture (SM) measurements is an important asset for agricultural activities, hydrologic studies, and environmental monitoring. The Advanced Microwave Scanning Radiometer 2 (AMSR2), which was launched in May 2012, has been providing SM data globally with a revisit period of two days. It is imperative to assess the quality of this data before performing any application. Since resources of accurate SM measurements are very limited in Puerto Rico, this research will assess the quality of the AMSR2 data by comparing it with ground-based measurements, as well as perform a downscaling technique to provide a better description of how the sensor perceives the surface soil moisture as it passes over the island. The comparison consisted of the evaluation of the mean error, root mean squared error, and the correlation coefficient. Two downscaling techniques were used, and their performances were studied. The results revealed that AMSR2 products tend to underestimate soil moisture. This is due to the extreme heterogeneous distributions of elevations, vegetation densities, soil types, and weather events on the island. This research provides a comprehensive study on the accuracy and potential of the AMSR2 products over Puerto Rico. Further studies are recommended to improve the AMSR2 products.

Highlights

Soil moisture (SM) content is the quantity of water accumulated in soil pores, usually recorded as percent or volumetric ratio for different depths (e.g., 5 cm, 10 cm, and 25 cm)
The maximum, minimum, mean, and standard deviation were calculated for each station, and all of the Advanced Microwave Scanning Radiometer 2 (AMSR2) pixels that were matched by distance, as previously explained
The comparison of AMSR2 soil moisture (SM) products at 25 km resolution with the Soil Climate Analysis Network (SCAN)–Natural Resources Conservation Service (NRCS) stations revealed that the AMSR2 spatial coverage of 25 km does not provide a good estimate of SM in Puerto Rico

Summary

Introduction

Soil moisture (SM) content is the quantity of water accumulated in soil pores, usually recorded as percent or volumetric ratio (e.g., cm3 /cm3 ) for different depths (e.g., 5 cm, 10 cm, and 25 cm). SM plays an important role in water cycles, hydrologic studies, agricultural activities, and environmental monitoring [1,2,3,4,5,6]. Hydrologic modeling systems are very sensitive to changes in SM values for applications involving flood control and drought assessment [1]. Best management practices and irrigation control can be optimized with continuous spatio-temporal SM measurements [7]. Predictions and results for environmental monitoring applications such as climate change and weather forecasting have a high dependency on the accuracy of the SM data [5,6,8]. The spatio-temporal availability of accurate SM measurements rely on the quality of the instruments, frequency of retrieval, and management of the data [2]. There are three options for acquiring SM content: ground-based measurements, modeling predictions, and remotely-sensed estimates [1,3]

Methods

Results

Conclusion