Towards an improved surface roughness parametrization model for soil moisture retrieval in road construction

Thi Mai Nguyen, Jeffrey P. Walker, Nan Ye, Jayantha Kodikara

Research output: Contribution to journalArticleResearchpeer-review


In passive microwave remote sensing, estimation of the surface roughness parameter is a significant obstacle for soil moisture (SM) retrieval. For a given SM content, the geometric soil surface roughness has been shown to have a large impact on the surface emission at L-band frequency, which affects the SM retrieval success when using the information observed from the radiometer, and is represented through the so-called the surface roughness parameter (<italic>HR</italic>). Moreover, no previous study has examined the effect of this factor in the context of road construction, where the geometric soil surface roughness is affected by the compaction process, resulting in a substantial change in roughness before and after compaction. Accordingly, a series of experiments at various compaction levels and SM contents were performed for a sand subgrade material in order to identify their effects on <italic>HR</italic>. The soil brightness temperature (TB) was measured using an L-band radiometer at different incidence angles and a laser profiler was used to measure the surface roughness standard deviation (&#x03C3;) before and after compaction. The results of this paper have demonstrated that incidence angle (&#x03B8;) and SM both affect <italic>HR</italic> and its relation with the geometric soil surface roughness. Importantly, these factors are not accounted for by existing models. Consequently, a modified surface roughness parameter (<italic>HR</italic>) model, based on the traditional Choudhury model, was developed to include the contribution of these two factors, and its impact on the accuracy of SM retrieval results tested. Specifically, it was shown that it is possible to obtain SM retrieval results with an accuracy of 0.04 cm3/cm3 at almost all incidence angles using either dual-polarization (both horizontal (H) and vertical polarization (V)) or only vertical polarization observations. The modified surface roughness parameter (<italic>HR</italic>) model has improved the performance of the SM retrieval model to achieve an accuracy of 0.04 cm3/cm3, whereas the traditional Choudhury model achieved an accuracy of only 0.05 cm3/cm3.

Original languageEnglish
Article number5300313
Number of pages13
JournalIEEE Transactions on Geoscience and Remote Sensing
Publication statusPublished - 2023


  • Compaction
  • L-band
  • L-band radiometer
  • Roads
  • Rough surfaces
  • sand subgrade
  • Soil
  • soil moisture
  • Surface roughness
  • surface roughness parameter
  • Surface waves

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