Estimating Soil Moisture Distributions across Small Farm Fields with ALOS/PALSAR

Yuki Kojima,Kosuke Noborio,Kazuo Oki,Masaru Mizoguchi

doi:10.1155/2016/4203783

Abstract

The ALOS (advanced land observing satellite) has an active microwave sensor, PALSAR (phased array L-band synthetic aperture radar), which has a fine resolution of 6.5 m. Because of the fine resolution, PALSAR provides the possibility of estimating soil moisture distributions in small farmlands. Making such small-scale estimates has not been available with traditional satellite remote sensing techniques. In this study, the relationship between microwave backscattering coefficient (σ) measured with PALSAR and ground-based soil moisture was determined to investigate the performance of PALSAR for estimating soil moisture distribution in a small-scale farmland. On the ground at a cabbage field in Japan in 2008, the soil moisture distribution of multiple soil layers was measured using time domain reflectometry when the ALOS flew over the field. Soil moisture in the 0–20 cm soil layer showed the largest correlation coefficient with σ (r = 0.403). The σ values also showed a strong correlation with the ground surface coverage ratio by cabbage plants. Our results suggested that PALSAR could estimate soil moisture distribution of the 0–20 cm soil layer across a bare field and a crop coverage ratio when crops were planted.

Highlights

Based on the 10-year Global Earth Observation System of Systems (GEOSS) implementation plan, integration of global earth observation data associated with climate change and hydrological cycle has been conducted with the cooperation of nearly 60 countries [1]
Using average volumetric water content measured with the various depths of time domain reflectometry (TDR) probes, we investigated how deep microwave from the phased array L-band synthetic aperture radar (PALSAR) single polarization mode penetrated in soil
We investigated how well the AOS/PALSAR estimated soil moisture distribution in a small-scale farmland

Summary

Introduction

Based on the 10-year Global Earth Observation System of Systems (GEOSS) implementation plan, integration of global earth observation data associated with climate change and hydrological cycle has been conducted with the cooperation of nearly 60 countries [1]. Previous studies using the PALSAR single polarization mode to estimate soil moisture were more or less focused on relatively large areas such as that by Susaki [20] estimating soil moisture distribution in noninundated paddy fields with the mesh size of 100 m and that by Sonobe et al [21] evaluating the averaged soil moisture of an entire farmland. To obtain a fundamental knowledge for estimating soil moisture with the PALSAR, we aimed in this study to establish a relationship between backscattering coefficients measured with the single polarization mode of PALSAR and volumetric water content, in small-scale farmlands. Using average volumetric water content measured with the various depths of TDR probes, we investigated how deep microwave from the PALSAR single polarization mode penetrated in soil. In addition to the volumetric water content, a relationship between backscattering coefficients and surface crop coverage was investigated to better understand the PALSAR application

Relationship between Microwave Reflection and Soil Moisture

Materials and Methods

Results and Discussion

Conclusions