Impacts of Radiometric Uncertainty and Weather-Related Surface Conditions on Soil Moisture Retrievals with Sentinel-1
The radiometric uncertainty of Synthetic Aperture Radar (SAR) observations and weather-related surface conditions caused by frozen conditions, snow and intercepted rain affect the backscatter (<inline-formula> <math display="inline"> <semantics> <msup> <mi>&am...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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MDPI AG
2019-08-01
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| Series: | Remote Sensing |
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| Online Access: | https://www.mdpi.com/2072-4292/11/17/2025 |
| _version_ | 1819001330559090688 |
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| author | Harm-Jan F. Benninga Rogier van der Velde Zhongbo Su |
| author_facet | Harm-Jan F. Benninga Rogier van der Velde Zhongbo Su |
| author_sort | Harm-Jan F. Benninga |
| collection | DOAJ |
| description | The radiometric uncertainty of Synthetic Aperture Radar (SAR) observations and weather-related surface conditions caused by frozen conditions, snow and intercepted rain affect the backscatter (<inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula>) observations and limit the accuracy of soil moisture retrievals. This study estimates Sentinel-1’s radiometric uncertainty, identifies the effects of weather-related surface conditions on <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> and investigates their impact on soil moisture retrievals for various conditions regarding soil moisture, surface roughness and incidence angle. Masking rules for the surface conditions that disturb <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> were developed based on meteorological measurements and timeseries of Sentinel-1 observations collected over five forests, five meadows and five cultivated fields in the eastern part of the Netherlands. The Sentinel-1 <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> observations appear to be affected by frozen conditions below an air temperature of 1<inline-formula> <math display="inline"> <semantics> <mrow> <msup> <mrow></mrow> <mo>∘</mo> </msup> <mi mathvariant="normal">C</mi> </mrow> </semantics> </math> </inline-formula>, snow during Sentinel-1’s morning overpasses on meadows and cultivated fields and interception after more than <inline-formula> <math display="inline"> <semantics> <mrow> <mn>1.8</mn> </mrow> </semantics> </math> </inline-formula> <inline-formula> <math display="inline"> <semantics> <mi mathvariant="normal">m</mi> </semantics> </math> </inline-formula><inline-formula> <math display="inline"> <semantics> <mi mathvariant="normal">m</mi> </semantics> </math> </inline-formula> of rain in the 12 h preceding a Sentinel-1 overpass, whereas dew was not found to be of influence. After the application of these masking rules, the radiometric uncertainty was estimated by the standard deviation of the seasonal anomalies timeseries of the Sentinel-1 forest <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> observations. By spatially averaging the <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> observations, the Sentinel-1 radiometric uncertainty improves from <inline-formula> <math display="inline"> <semantics> <mrow> <mn>0.85</mn> </mrow> </semantics> </math> </inline-formula> dB for a surface area of <inline-formula> <math display="inline"> <semantics> <mrow> <mn>0.25</mn> </mrow> </semantics> </math> </inline-formula><inline-formula> <math display="inline"> <semantics> <mrow> <mi mathvariant="normal">h</mi> <mi mathvariant="normal">a</mi> </mrow> </semantics> </math> </inline-formula> to <inline-formula> <math display="inline"> <semantics> <mrow> <mn>0.30</mn> </mrow> </semantics> </math> </inline-formula> dB for 10 <inline-formula> <math display="inline"> <semantics> <mrow> <mi mathvariant="normal">h</mi> <mi mathvariant="normal">a</mi> </mrow> </semantics> </math> </inline-formula> for the VV polarization and from <inline-formula> <math display="inline"> <semantics> <mrow> <mn>0.89</mn> </mrow> </semantics> </math> </inline-formula> dB to <inline-formula> <math display="inline"> <semantics> <mrow> <mn>0.36</mn> </mrow> </semantics> </math> </inline-formula> dB for the VH polarization, following approximately an inverse square root dependency on the surface area over which the <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> observations are averaged. Deviations in <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> were combined with the <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> sensitivity to soil moisture as simulated with the Integral Equation Method (IEM) surface scattering model, which demonstrated that both the disturbing effects by the weather-related surface conditions (if not masked) and radiometric uncertainty have a significant impact on the soil moisture retrievals from Sentinel-1. The soil moisture retrieval uncertainty due to radiometric uncertainty ranges from <inline-formula> <math display="inline"> <semantics> <mrow> <mn>0.01</mn> </mrow> </semantics> </math> </inline-formula><inline-formula> <math display="inline"> <semantics> <msup> <mi mathvariant="normal">m</mi> <mn>3</mn> </msup> </semantics> </math> </inline-formula><inline-formula> <math display="inline"> <semantics> <msup> <mi mathvariant="normal">m</mi> <mrow> <mo>−</mo> <mn>3</mn> </mrow> </msup> </semantics> </math> </inline-formula> up to <inline-formula> <math display="inline"> <semantics> <mrow> <mn>0.17</mn> </mrow> </semantics> </math> </inline-formula><inline-formula> <math display="inline"> <semantics> <msup> <mi mathvariant="normal">m</mi> <mn>3</mn> </msup> </semantics> </math> </inline-formula><inline-formula> <math display="inline"> <semantics> <msup> <mi mathvariant="normal">m</mi> <mrow> <mo>−</mo> <mn>3</mn> </mrow> </msup> </semantics> </math> </inline-formula> for wet soils and small surface areas. The impacts on soil moisture retrievals are found to be weakly dependent on the surface roughness and the incidence angle, and strongly dependent on the surface area (or the <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> disturbance caused by a weather-related surface condition for a specific land cover type) and the soil moisture itself. |
| first_indexed | 2024-12-20T22:47:30Z |
| format | Article |
| id | doaj.art-6c879dd545b94a679f43ccefa087dd4d |
| institution | Directory Open Access Journal |
| issn | 2072-4292 |
| language | English |
| last_indexed | 2024-12-20T22:47:30Z |
| publishDate | 2019-08-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Remote Sensing |
| spelling | doaj.art-6c879dd545b94a679f43ccefa087dd4d2022-12-21T19:24:21ZengMDPI AGRemote Sensing2072-42922019-08-011117202510.3390/rs11172025rs11172025Impacts of Radiometric Uncertainty and Weather-Related Surface Conditions on Soil Moisture Retrievals with Sentinel-1Harm-Jan F. Benninga0Rogier van der Velde1Zhongbo Su2Department of Water Resources, Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, P.O. Box 217, 7500 AE Enschede, The NetherlandsDepartment of Water Resources, Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, P.O. Box 217, 7500 AE Enschede, The NetherlandsDepartment of Water Resources, Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, P.O. Box 217, 7500 AE Enschede, The NetherlandsThe radiometric uncertainty of Synthetic Aperture Radar (SAR) observations and weather-related surface conditions caused by frozen conditions, snow and intercepted rain affect the backscatter (<inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula>) observations and limit the accuracy of soil moisture retrievals. This study estimates Sentinel-1’s radiometric uncertainty, identifies the effects of weather-related surface conditions on <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> and investigates their impact on soil moisture retrievals for various conditions regarding soil moisture, surface roughness and incidence angle. Masking rules for the surface conditions that disturb <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> were developed based on meteorological measurements and timeseries of Sentinel-1 observations collected over five forests, five meadows and five cultivated fields in the eastern part of the Netherlands. The Sentinel-1 <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> observations appear to be affected by frozen conditions below an air temperature of 1<inline-formula> <math display="inline"> <semantics> <mrow> <msup> <mrow></mrow> <mo>∘</mo> </msup> <mi mathvariant="normal">C</mi> </mrow> </semantics> </math> </inline-formula>, snow during Sentinel-1’s morning overpasses on meadows and cultivated fields and interception after more than <inline-formula> <math display="inline"> <semantics> <mrow> <mn>1.8</mn> </mrow> </semantics> </math> </inline-formula> <inline-formula> <math display="inline"> <semantics> <mi mathvariant="normal">m</mi> </semantics> </math> </inline-formula><inline-formula> <math display="inline"> <semantics> <mi mathvariant="normal">m</mi> </semantics> </math> </inline-formula> of rain in the 12 h preceding a Sentinel-1 overpass, whereas dew was not found to be of influence. After the application of these masking rules, the radiometric uncertainty was estimated by the standard deviation of the seasonal anomalies timeseries of the Sentinel-1 forest <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> observations. By spatially averaging the <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> observations, the Sentinel-1 radiometric uncertainty improves from <inline-formula> <math display="inline"> <semantics> <mrow> <mn>0.85</mn> </mrow> </semantics> </math> </inline-formula> dB for a surface area of <inline-formula> <math display="inline"> <semantics> <mrow> <mn>0.25</mn> </mrow> </semantics> </math> </inline-formula><inline-formula> <math display="inline"> <semantics> <mrow> <mi mathvariant="normal">h</mi> <mi mathvariant="normal">a</mi> </mrow> </semantics> </math> </inline-formula> to <inline-formula> <math display="inline"> <semantics> <mrow> <mn>0.30</mn> </mrow> </semantics> </math> </inline-formula> dB for 10 <inline-formula> <math display="inline"> <semantics> <mrow> <mi mathvariant="normal">h</mi> <mi mathvariant="normal">a</mi> </mrow> </semantics> </math> </inline-formula> for the VV polarization and from <inline-formula> <math display="inline"> <semantics> <mrow> <mn>0.89</mn> </mrow> </semantics> </math> </inline-formula> dB to <inline-formula> <math display="inline"> <semantics> <mrow> <mn>0.36</mn> </mrow> </semantics> </math> </inline-formula> dB for the VH polarization, following approximately an inverse square root dependency on the surface area over which the <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> observations are averaged. Deviations in <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> were combined with the <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> sensitivity to soil moisture as simulated with the Integral Equation Method (IEM) surface scattering model, which demonstrated that both the disturbing effects by the weather-related surface conditions (if not masked) and radiometric uncertainty have a significant impact on the soil moisture retrievals from Sentinel-1. The soil moisture retrieval uncertainty due to radiometric uncertainty ranges from <inline-formula> <math display="inline"> <semantics> <mrow> <mn>0.01</mn> </mrow> </semantics> </math> </inline-formula><inline-formula> <math display="inline"> <semantics> <msup> <mi mathvariant="normal">m</mi> <mn>3</mn> </msup> </semantics> </math> </inline-formula><inline-formula> <math display="inline"> <semantics> <msup> <mi mathvariant="normal">m</mi> <mrow> <mo>−</mo> <mn>3</mn> </mrow> </msup> </semantics> </math> </inline-formula> up to <inline-formula> <math display="inline"> <semantics> <mrow> <mn>0.17</mn> </mrow> </semantics> </math> </inline-formula><inline-formula> <math display="inline"> <semantics> <msup> <mi mathvariant="normal">m</mi> <mn>3</mn> </msup> </semantics> </math> </inline-formula><inline-formula> <math display="inline"> <semantics> <msup> <mi mathvariant="normal">m</mi> <mrow> <mo>−</mo> <mn>3</mn> </mrow> </msup> </semantics> </math> </inline-formula> for wet soils and small surface areas. The impacts on soil moisture retrievals are found to be weakly dependent on the surface roughness and the incidence angle, and strongly dependent on the surface area (or the <inline-formula> <math display="inline"> <semantics> <msup> <mi>σ</mi> <mn>0</mn> </msup> </semantics> </math> </inline-formula> disturbance caused by a weather-related surface condition for a specific land cover type) and the soil moisture itself.https://www.mdpi.com/2072-4292/11/17/2025Sentinel-1radiometric uncertaintydisturbing surface conditionsmasking rulessoil moisture |
| spellingShingle | Harm-Jan F. Benninga Rogier van der Velde Zhongbo Su Impacts of Radiometric Uncertainty and Weather-Related Surface Conditions on Soil Moisture Retrievals with Sentinel-1 Remote Sensing Sentinel-1 radiometric uncertainty disturbing surface conditions masking rules soil moisture |
| title | Impacts of Radiometric Uncertainty and Weather-Related Surface Conditions on Soil Moisture Retrievals with Sentinel-1 |
| title_full | Impacts of Radiometric Uncertainty and Weather-Related Surface Conditions on Soil Moisture Retrievals with Sentinel-1 |
| title_fullStr | Impacts of Radiometric Uncertainty and Weather-Related Surface Conditions on Soil Moisture Retrievals with Sentinel-1 |
| title_full_unstemmed | Impacts of Radiometric Uncertainty and Weather-Related Surface Conditions on Soil Moisture Retrievals with Sentinel-1 |
| title_short | Impacts of Radiometric Uncertainty and Weather-Related Surface Conditions on Soil Moisture Retrievals with Sentinel-1 |
| title_sort | impacts of radiometric uncertainty and weather related surface conditions on soil moisture retrievals with sentinel 1 |
| topic | Sentinel-1 radiometric uncertainty disturbing surface conditions masking rules soil moisture |
| url | https://www.mdpi.com/2072-4292/11/17/2025 |
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