MAPPING AND MONITORING RICE AREAS IN CENTRAL LUZON, PHILIPPINES USING X AND C-BAND SAR IMAGERY

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Research areas:
Year:
2016
Type of Publication:
In Proceedings
Keywords:
rice mapping, TerraSAR-X, Sentinel-1A, radar
Authors:
Raviz, Jeny; Laborte, Alice; Barbieri, Massimo; Mabalay, Mary Rose; Garcia, Cornelia; Bibar, Jesiree Elena Ann; Mabalot, Pristine; Gonzaga, Harvey
Abstract:
This study aims to assess the use of X- and C-band Synthetic Aperture Radar (SAR) for mapping rice areas. Specifically, we used TerraSAR-X (TSX, X-band, HH polarization) and Sentinel-1A (S1A, C-band, VV and VH polarizations) data from two cropping seasons: 2015 wet season (WS, June to October) and 2016 dry season (DS, October to February) in Central Luzon, Philippines. A total of 130 TSX and 80 S1A images were used to map rice areas in these two seasons. We used the image processing software MAPscape-RICE® to process SAR images and to generate the rice maps. The procedure involved three main steps: (1) basic processing, (2) rice area mapping, and (3) validation. In basic processing (step 1), original SAR data were converted to terrain-geocoded images (backscatter δo values). The multi-temporal SAR signature from step 1 were then analysed to set the appropriate thresholds following a rule-based rice detection algorithm (step 2). The rules for rice detection were based on a well-studied temporal signature of rice gathered from monitored sites and its relationship with SAR backscatter. Although the same procedure was followed, different thresholds were applied to the SAR data. Accuracies were compared using ground observations collected towards the end of each growing season (step 3). Based on 126 ground observations gathered in the study area in 2015 WS, the overall accuracies of the rice maps generated were 86% (kappa=0.71) for TSX, 80% (kappa=0.60) for S1A-VV, and 76% (kappa=0.52) for S1A-VH. In 2016 DS, the overall accuracies based on 132 ground observations were 86% for TSX, 82% for S1A-VV and 70% for S1A-VH. From this study, TSX consistently provided the highest accuracies and S1A-VH the lowest. S1A-VH may not be useful for mapping rice areas. S1A-VV, on the other hand, still provided high accuracies. Better thresholds will be explored to improve accuracies.
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