A new soil freeze/thaw discriminant algorithm using AMSR-E passive microwave imagery

Abstract

Abstract:The soil freeze-thaw controls the hydrological and carbon cycling and thus affects water and energy exchanges at land surface. This article reported a newly developed algorithm for distinguishing the freeze/thaw status of surface soil. The algorithm was based on information from Advanced Microwave Scanning Radiometer Enhanced (AMSR-E) which records brightness temperature (Tb) in the afternoon and after midnight. The criteria and discriminant functions were obtained from both radiometer observations and model simulations. First of all, the microwave radiation from freeze-thaw soil was examined by carrying out experimental measurements at 18Ð7 and 36Ð5 GHz using a Truck-mounted Multi-frequency Microwave Radiometer (TMMR) in the Heihe River of China. The experimental results showed that the soil moisture is a key component that differentiates the microwave radiation behaviours during the freeze-thaw process, and the differences in soil temperature and emissivity between frozen and thawed soils were found to be the most important criteria. Secondly, a combined model was developed to consider the impacts of complex ground surface conditions on the discrimination. The model simulations quite followed the trend of in situ observations with an overall relation coefficient (R) of approximately 0Ð88. Finally, the ratio of Tb18Ð7H (horizontally polarized Tb at 18Ð7 GHz) to Tb36Ð5V was considered primarily as the quasi-emissivity, which is more reasonable and explicit in measuring the microwave radiation changes in soil freezing and thawing than the spectral gradient. By combining Tb36Ð5V to indicate the soil temperature variety, a Fisher linear discrimination analysis was used to establish the discriminant functions. After being corrected by TMMR measurements, the new discriminant algorithm had an overall accuracy of 86% when validated by 4-cm soil temperature. The multi-year discriminant results also provided a good agreement with the classification map of frozen ground in China.

Attribution of divergent northern vegetation growth responses to lengthening non-frozen seasons using satellite optical-NIR and microwave remote sensing

“…The satellite microwave FT signal senses the predominant FR or non-frozen (NF) status of water in surface soil and vegetation canopy layers Zhao et al 2011), and has been linked to FR temperature constraints to vegetation productivity, landscape water mobility, and land-atmosphere carbon exchange over the HNL domain McDonald et al 2004;Zhang et al 2011). Kim et al (2012) applied the satellite FT record and documented significant Northern Hemisphere trends of lengthening NF seasons consistent with recent global warming from 1979 to 2008.…”

Gravimetric Vegetation Water Content Estimation for Corn Using L-Band Bi-Angular, Dual-Polarized Brightness Temperatures and Leaf Area Index

“…At the passive microwave footprint scale, the temperatures of the short vegetation and soil can be considered equal, i.e., = = [16,17]. Moreover, the observed vegetation canopy signals represent the overall effect of the mixture of the different vegetation canopy types present.…”

A Parameterized Microwave Emissivity Model for Bare Soil Surfaces

“…The passive microwave radiometer used for this experiment was a truck-mounted multi-frequency microwave radiometer (TMMR) with an articulated arm serving as the sensor platform [32,33]. The TMMR was operated in dual polarization at frequencies of 6.925, 10.65, 18.7, and 36.5 GHz (C, X, Ku, and Ka bands, respectively).…”

“…The TMMR was operated in dual polarization at frequencies of 6.925, 10.65, 18.7, and 36.5 GHz (C, X, Ku, and Ka bands, respectively). The instrument calibration was conducted using a four-point calibration procedure before the experiments [33]. A sensitivity of approximately ±0.5 K and an accuracy of ±1 K were achieved after calibration [32,34].…”