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Article

Analyses of Namibian Seasonal Salt Pan Crust Dynamics and Climatic Drivers Using Landsat 8 Time-Series and Ground Data

1
Helmholtz Center Potsdam, GFZ German Research Center for Geosciences, Section 1.4: Remote Sensing and Geoinformatics, Telegrafenberg, 14473 Potsdam, Germany
2
Institute of Geoscience, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany
*
Author to whom correspondence should be addressed.
Remote Sens. 2020, 12(3), 474; https://doi.org/10.3390/rs12030474
Received: 31 December 2019 / Revised: 21 January 2020 / Accepted: 28 January 2020 / Published: 3 February 2020
(This article belongs to the Special Issue Remote Sensing in Dryland Assessment and Monitoring)
Salt pans are highly dynamic environments that are difficult to study by in situ methods because of their harsh climatic conditions and large spatial areas. Remote sensing can help to elucidate their environmental dynamics and provide important constraints regarding their sedimentological, mineralogical, and hydrological evolution. This study utilizes spaceborne multitemporal multispectral optical data combined with spectral endmembers to document spatial distribution of surface crust types over time on the Omongwa pan located in the Namibian Kalahari. For this purpose, 49 surface samples were collected for spectral and mineralogical characterization during three field campaigns (2014–2016) reflecting different seasons and surface conditions of the salt pan. An approach was developed to allow the spatiotemporal analysis of the salt pan crust dynamics in a dense time-series consisting of 77 Landsat 8 cloud-free scenes between 2014 and 2017, covering at least three major wet–dry cycles. The established spectral analysis technique Sequential Maximum Angle Convex Cone (SMACC) extraction method was used to derive image endmembers from the Landsat time-series stack. Evaluation of the extracted endmember set revealed that the multispectral data allowed the differentiation of four endmembers associated with mineralogical mixtures of the crust’s composition in dry conditions and three endmembers associated with flooded or muddy pan conditions. The dry crust endmember spectra have been identified in relation to visible, near infrared, and short-wave infrared (VNIR–SWIR) spectroscopy and X-ray diffraction (XRD) analyses of the collected surface samples. According these results, the spectral endmembers are interpreted as efflorescent halite crust, mixed halite–gypsum crust, mixed calcite quartz sepiolite crust, and gypsum crust. For each Landsat scene the spatial distribution of these crust types was mapped with the Spectral Angle Mapper (SAM) method and significant spatiotemporal dynamics of the major surface crust types were observed. Further, the surface crust dynamics were analyzed in comparison with the pan’s moisture regime and other climatic parameters. The results show that the crust dynamics are mainly driven by flooding events in the wet season, but are also influenced by temperature and aeolian activity in the dry season. The approach utilized in this study combines the advantages of multitemporal satellite data for temporal event characterization with advantages from hyperspectral methods for the image and ground data analyses that allow improved mineralogical differentiation and characterization. View Full-Text
Keywords: salt pan; playa; spectral analysis; crust; saline pan cycle; evaporites; time-series mapping salt pan; playa; spectral analysis; crust; saline pan cycle; evaporites; time-series mapping
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MDPI and ACS Style

Milewski, R.; Chabrillat, S.; Bookhagen, B. Analyses of Namibian Seasonal Salt Pan Crust Dynamics and Climatic Drivers Using Landsat 8 Time-Series and Ground Data. Remote Sens. 2020, 12, 474. https://doi.org/10.3390/rs12030474

AMA Style

Milewski R, Chabrillat S, Bookhagen B. Analyses of Namibian Seasonal Salt Pan Crust Dynamics and Climatic Drivers Using Landsat 8 Time-Series and Ground Data. Remote Sensing. 2020; 12(3):474. https://doi.org/10.3390/rs12030474

Chicago/Turabian Style

Milewski, Robert, Sabine Chabrillat, and Bodo Bookhagen. 2020. "Analyses of Namibian Seasonal Salt Pan Crust Dynamics and Climatic Drivers Using Landsat 8 Time-Series and Ground Data" Remote Sensing 12, no. 3: 474. https://doi.org/10.3390/rs12030474

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