Determination of the Optimal Mounting Depth for Calculating Effective Soil Temperature at L-Band: Maqu Case

Abstract

Effective soil temperature T e f f is one of the basic parameters in passive microwave remote sensing of soil moisture. At present, dedicated satellite soil moisture monitoring missions use the L-band as the operating frequency. However, T e f f at the L-band is strongly affected by soil moisture and temperature profiles. Recently, a two-layer scheme and a corresponding multilayer form have been developed to accommodate such influences. In this study, the soil moisture/temperature data collected and simulated by the Noah land surface model across the Maqu Network are used to verify the newly developed schemes. There are two key findings. Firstly, the new two-layer scheme is able to assess which site provides relatively higher accuracy when estimating T e f f . It is found that, on average, nearly 20% of the T e f f signal cannot be captured by the Maqu Network, in the currently assumed common installation configuration. This knowledge is important, since the spatial averaged brightness temperature (a function of T e f f ) is used to determine soil moisture. Secondly, the developed method has made it possible to identify that the optimal mounting depths for the observation pair are 5 cm and 20 cm for calculating T e f f at the center station in the Maqu Network. It has been suggested that the newly developed method can provide an objective way to configure an optimal soil moisture/temperature network and improve the representativeness of the existing networks regarding the calculation of T e f f .

Estimation of Penetration Depth from Soil Effective Temperature in Microwave Radiometry

“…However L-band radiometry for monitoring soil moisture is strongly affected by the soil temperature and soil moisture [15,16], which usually leads to questions on where the satellite is exactly sensing [17][18][19]. Corresponding to the satellite missions, plenty of in situ soil moisture monitoring networks have been established to calibrate and validate (Cal/Val) L-band brightness temperature (T b ) or soil moisture data [20].…”

“…In general, all current two-layer T e f f schemes use a weighting function for the soil temperature between upper layer and deeper layer. Such weighting function can be a constant [29], a fitting function [30,31], or an exponential function [15,16]. The weighting function is supposed to reflect the impact of soil moisture on the soil effective temperature.…”

Preface: Land Surface Processes and Interactions—From HCMM to Sentinel Missions and Beyond

“…From the perspective of radiative transfer theory, Lv et al [27] discussed how to determine the optimal mounting depth of soil moisture and soil temperature (SMST) sensors, for calculating soil effective temperature (T eff ) from satellite microwave sensors at the L-band, based on Lv's multilayer T eff scheme [28,29]. It was found that, on average, nearly 20% of the T eff signal cannot be captured by the Maqu in situ SMST network, using the currently assumed common installation configurations (i.e., 5 cm, 10 cm, 20 cm, 40 cm, and 80 cm).…”

Soil effective temperature and its application in passive remote sensing of soil moisture at L-Band

“…Corresponding to the satellite missions, plenty of in situ soil moisture monitoring networks have been established to calibrate and validate (Cal/Val) L-band brightness temperatures ( b T ) or derived soil moisture [24]. L-band emission is however strongly affected by both soil temperature and soil moisture [167,168], which usually leads to questions on what the satellite is exactly sensing [90,169,170]. Usually, soil moisture and soil temperature sensors are installed at certain depths based on different preferences, e.g., 2.5 cm, 5 cm, 10 cm, or deeper, to match numerical simulations of soil moisture and soil temperature.…”

“…Two-layer eff T schemes contribute a weighted average of the soil temperature of an upper layer and a deeper layer. Such weighting functions can be a constant [86], a fitting function [80] and [87], or an exponential function [167,168]. The weighting function is supposed to reflect the impact of soil moisture on the soil effective temperature.…”