Agricultural Sciences and Applications Group, National Remote Sensing Centre, Balanagar, Hyderabad, 500625, India,
Environ Monit Assess. 2013 Dec;185(12):9889-902. doi: 10.1007/s10661-013-3299-8. Epub 2013 Jun 21.
Early season or crop-planting-period (ES/CPP) drought conditions have become a recurrent phenomenon in tropical countries like India, due to fluctuations in the time of onset and progression of monsoon rains. ES/CPP agricultural drought assessment is a major challenge because of the difficulties in the generation of operational products on soil moisture at larger scales. The present study analyzed the Shortwave Angle Slope Index (SASI) derived from Near Infrared and Shortwave Infrared data of Moderate Resolution Imaging Spectroradiometer, for tracking surface moisture changes and assessing the agricultural drought conditions during ES/CPP, over Andhra Pradesh state, India. It was found that in-season progression of SASI was well correlated with rainfall and crop planting patterns in different districts of the study area state in both drought and normal years. Rainfall occurrence, increase in crop planted area, and decrease in SASI were in chronological synchronization in the season. Change in SASI from positive to negative values is a unique indication of dryness to wetness shift in the season. Duration of positive SASI values indicated the persistence of agricultural drought in the crop planting period. Mean SASI values were able to discriminate an area which was planted in normal year and unplanted in drought year. SASI thresholds provide an approximate and rapid estimate of the crop planting favorable area in a region which is useful to assess the impact of drought. Thus, SASI is a potential index to strengthen the existing operational drought monitoring systems. Further work needs to be on the integration of multiple parameters-SASI, soil texture, soil depth, rainfall and cropping pattern, to evolve a geospatial product on crop planting favorable areas. Such products pave the way for quantification of drought impact on agriculture in the early part of the season, which is a major inadequacy in the current drought monitoring system.
早期季节或作物种植期（ES/CPP）干旱条件已成为印度等热带国家的一种反复出现的现象，这是由于季风降雨开始和推进时间的波动所致。由于在较大尺度上生成土壤湿度业务产品的困难，ES/CPP 农业干旱评估是一项主要挑战。本研究分析了中分辨率成像光谱仪近红外和短波红外数据得出的短波角斜率指数（SASI），以跟踪表面水分变化并评估印度安得拉邦 ES/CPP 期间的农业干旱状况。结果表明，在干旱和正常年份，SASI 的季节内进展与不同地区的降雨和作物种植模式密切相关。降雨发生、种植面积增加和 SASI 减少在季节中具有时间同步性。SASI 从正值变为负值的变化是季节干湿转换的独特指示。正值 SASI 的持续时间表明作物种植期农业干旱的持续时间。平均 SASI 值能够区分在正常年份种植而在干旱年份未种植的区域。SASI 阈值可提供区域内有利于种植作物的近似快速估计，这有助于评估干旱的影响。因此，SASI 是增强现有业务干旱监测系统的潜在指标。进一步的工作需要整合多个参数-SASI、土壤质地、土壤深度、降雨和种植模式，以生成有利于作物种植的地理空间产品。这些产品为量化季节早期干旱对农业的影响铺平了道路，这是当前干旱监测系统的主要不足。
