Karthikeyan, L and Pan, M and Kumar, DN and Wood, EF (2020) Effect of structural uncertainty in passive microwave soil moisture retrieval algorithm. In: Sensors (Switzerland), 20 (4).
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Abstract
Passive microwave sensors use a radiative transfer model (RTM) to retrieve soil moisture (SM) using brightness temperatures (TB) at low microwave frequencies. Vegetation optical depth (VOD) is a key input to the RTM. Retrieval algorithms can analytically invert the RTM using dual-polarized TB measurements to retrieve the VOD and SM concurrently. Algorithms in this regard typically use the τ-ω types of models, which consist of two third-order polynomial equations and, thus, can have multiple solutions. Through this work, we find that uncertainty occurs due to the structural indeterminacy that is inherent in all τ-ω types of models in passive microwave SM retrieval algorithms. In the process, a new analytical solution for concurrent VOD and SM retrieval is presented, along with two widely used existing analytical solutions. All three solutions are applied to a fixed framework of RTM to retrieve VOD and SM on a global scale, using X-band Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) TB data. Results indicate that, with structural uncertainty, there ensues a noticeable impact on the VOD and SM retrievals. In an era where the sensitivity of retrieval algorithms is still being researched, we believe the structural indeterminacy of RTM identified here would contribute to uncertainty in the soil moisture retrievals. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
| Item Type: | Journal Article |
|---|---|
| Publication: | Sensors (Switzerland) |
| Publisher: | MDPI AG |
| Additional Information: | The copyright for this article belongs to the Authors. |
| Keywords: | Microwaves; Polynomials; Radiative transfer; Soil mechanics; Soil moisture; Video on demand, Equifinality; Passive microwaves; Radiative transfer model; Retrieval algorithms; Uncertainty, Microwave sensors |
| Department/Centre: | Division of Mechanical Sciences > Civil Engineering |
| Date Deposited: | 24 Jan 2023 11:34 |
| Last Modified: | 24 Jan 2023 11:34 |
| URI: | https://eprints.iisc.ac.in/id/eprint/79445 |
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