Active and passive microwave signatures of diurnal soil freeze-thaw transitions on the Tibetan Plateau

Donghai Zheng*, Xin Li, Jun Wen, J.G. Hofste, R. van der Velde, Xin Wang, Zuoliang Wang, Xiaojing Bai, Mike Schwank, Zhongbo Su

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

Active and passive microwave characteristics of diurnal soil freeze-thaw transitions and their relationships are crucial for developing retrieval algorithms of the soil liquid water content (θliq) and freeze/thaw state, which, however, have been less explored. This study investigates these microwave characteristics and relationships via analysis of ground-based measurements of brightness temperature (TB) and backscattering coefficients (σ⁰) in combination with simulations performed with the Tor Vergata discrete radiative transfer model. Both an L-band (1.4 GHz) radiometer ELBARA-III and a wide-band (1-10 GHz) scatterometer are installed in a seasonally frozen Tibetan meadow ecosystem to measure diurnal variations of TB and copolarized σ⁰ at both hh (σhh⁰) and vv (σ vv⁰) polarizations. Analysis of measurements collected between December 2017 and March 2018 shows that 1) diurnal cycles are observed in both TB and σ ⁰ due to the change in surface θliq caused by diurnal soil freeze-thaw transitions; 2) a negatively linear relationship is found between e and σ⁰ regardless of frequency, polarization combinations, and observation angles; 3) slopes (β ) of linearly fit equations between eH and σhh⁰ decrease with increasing observation angles of ELBARA-III, while the ones between eV and σvv⁰ increase with increasing observation angles; and 4) correlations between e and σ⁰ increase with decreasing microwave frequency of σ⁰ measurements and ELBARA-III observation angles, and magnitudes of diurnal σ⁰ cycles also increase with decreasing microwave frequency. Moreover, the calibrated Tor Vergata model shows capability to reproduce both diurnal e and σ⁰ variations as well as to quantify their relationships at different frequencies and observation angles.
Original languageEnglish
Pages (from-to)1-14
Number of pages14
JournalIEEE transactions on geoscience and remote sensing
DOIs
Publication statusE-pub ahead of print/First online - 8 Jul 2021

Keywords

  • Microwave radiometry
  • Microwave measurement
  • Soil measurements
  • Temperature measurement
  • Radar measurements
  • Electromagnetic heating
  • Spaceborne radar
  • ITC-ISI-JOURNAL-ARTICLE

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