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Remote Sens. 2018, 10(4), 611; https://doi.org/10.3390/rs10040611

Detecting Trends in Wetland Extent from MODIS Derived Soil Moisture Estimates

Karttur AB, Birger Jarlsgatan 102b, 11420 Stockholm, Sweden
Received: 28 February 2018 / Revised: 9 April 2018 / Accepted: 12 April 2018 / Published: 15 April 2018
(This article belongs to the Special Issue Remote Sensing of Peatlands)
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Abstract

A soil wetness index for optical satellite images, the Transformed Wetness Index (TWI) is defined and evaluated against ground sampled soil moisture. Conceptually, TWI is formulated as a non-linear normalized difference index from orthogonalized vectors representing soil and water conditions, with the vegetation signal removed. Compared to 745 ground sites with in situ measured soil moisture, TWI has a globally estimated Random Mean Square Error of 14.0 (v/v expressed as percentage), which reduces to 8.5 for unbiased data. The temporal variation in soil moisture is significantly captured at 4 out of 10 stations, but also fails for 2 to 3 out of 10 stations. TWI is biased by different soil mineral compositions, dense vegetation and shadows, with the latter two most likely also causing the failure of TWI to capture soil moisture dynamics. Compared to soil moisture products from microwave brightness temperature data, TWI performs slightly worse, but has the advantages of not requiring ancillary data, higher spatial resolution and a relatively simple application. TWI has been used for wetland and peatland mapping in previously published studies but is presented in detail in this article, and then applied for detecting changes in soil moisture for selected tropical regions between 2001 and 2016. Sites with significant changes are compared to a published map of global tropical wetlands and peatlands. View Full-Text
Keywords: soil moisture; MODIS; wetlands; peatlands; change detection; Transformed Wetness Index (TWI) soil moisture; MODIS; wetlands; peatlands; change detection; Transformed Wetness Index (TWI)
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Gumbricht, T. Detecting Trends in Wetland Extent from MODIS Derived Soil Moisture Estimates. Remote Sens. 2018, 10, 611.

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