International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences
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Volume XLII-3/W2
Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci., XLII-3/W2, 151–155, 2017
https://doi.org/10.5194/isprs-archives-XLII-3-W2-151-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci., XLII-3/W2, 151–155, 2017
https://doi.org/10.5194/isprs-archives-XLII-3-W2-151-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.

  16 Nov 2017

16 Nov 2017

MONITORING THE IMPACTS OF EL NIÑO ON THE EXTENT OF CULTIVATED FIELDS USING SAR DATA AROUND THE AGRICULTURAL REGION OF THE FREE STATE, SOUTH AFRICA

A. Ngie1,2, S. Tesfamichael1, and F. Ahmed2 A. Ngie et al.
  • 1Department of Geography, Environmental management and Energy Studies, University of Johannesburg, P.O. Box 524 Auckland Park Johannesburg, 2006, South Africa
  • 2School of Geography, Archaeology and Environmental Studies, University of the Witwatersrand, Private Bag 3, WITS, 2050, South Africa

Keywords: Backscatter, cultivated fields, El Niño, sensitivity, Sentinel-1

Abstract. There is continuous challenge in crop monitoring from erratic climatic phenomena such as irregular rainfall episodes during required farming seasons or cloud cover. Remote sensing has offered vital support in the monitoring of such scenarios and informs relevant authorities for better decision making. While optical sensors measure the greenness of vegetation to enable monitoring of its status, their usage is constrained by the continuous cloud cover during crop growth seasons in sub Saharan Africa. Synthetic aperture radar data (SAR) are on the other hand capable of penetrating clouds and are sensitive to the structure and moisture content of target features, thereby providing complementary information for monitoring crop cultivated fields. This study sought to evaluate the sensitivity of Sentinel-1 SAR data to the status of cultivated crop fields that experienced varying rainfall amounts between 2015/2016 and 2016/2017 growing seasons as a result of El Niño induced drought in 2015. Dual polarization composites per season were classified and through sample farms delineated from Google Earth image, backscatter values were extracted for statistical comparisons. The two sample t-test was applied to test significance of the differences between the two seasons at the level of farm status. Results showed an overall significant difference (p-value of 0.003 < 0.005) in SAR backscatter sensitivity to cultivated crop fields during and after the El Niño phenomenon. While these results are encouraging for areas that experience clouds during growing seasons, further improvements can be expected by factoring in other variables such as topographic and moisture conditions of farms.