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

1 Citation (Scopus)
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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
Article number4301814
Number of pages14
JournalIEEE transactions on geoscience and remote sensing
DOIs
Publication statusPublished - 8 Jul 2021

Keywords

  • Microwave radiometry
  • Microwave measurement
  • Soil measurements
  • Temperature measurement
  • Radar measurements
  • Electromagnetic heating
  • Spaceborne radar
  • ITC-ISI-JOURNAL-ARTICLE
  • 22/1 OA procedure

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