遥感干旱指数在洛川苹果干旱监测中的适用性分析

目前对苹果干旱研究较少且主要运用站点数据，对空间信息表征有限，遥感干旱指数可用于大范围干旱时空动态监测，但在苹果干旱监测中的适用性还有待研究。基于2014~2018年MODIS反射率、地表温度以及地表覆被数据，结合土壤湿度数据和野外调查资料，分析洛川苹果区温度植被干旱指数（TVDI）、归一化植被水分指数（NDWI）、植被供水指数（VSWI）与10 cm深度土壤湿度（SM）的一致性，探索遥感干旱指标对土壤干湿状况表征能力，并进一步研究遥感干旱指标对干旱响应敏感时段。结果表明：①由增强型植被指数（EVI）计算的VSWI与SM的时空一致性最好，其在2014、2017年表现出的干旱特征与实际旱情相符；②VSWI（EVI）和TVDI（EVI）与SM的相关性分别高于VSWI（NDVI）和TVDI（NDVI）与SM的相关性，使用EVI能提高VSWI和TVDI对干旱的表征能力；③TVDI、NDWI、VSWI对SM存在不同时间的反应滞后，滞后3时相（24 d）的VSWI（EVI）与SM的相关性最高，而NDWI对SM滞后时间短，对干旱响应较及时，结合VSWI（EVI）和NDWI可能更有利于监测苹果干旱；④在不同苹果生育期，遥感指标对土壤湿度敏感性不同，VSWI在不同生育期敏感性差异最明显：新梢旺长期（5、6月）对土壤湿度敏感性高于萌芽开花期、果实膨大期、成熟期；该结果符合洛川县苹果不同生育期需水规律和洛川降水、干旱发生特征。研究结果可为遥感监测苹果干旱提供参考依据。

Applicability Analysis of Remote Sensing based Drought Indices in Drought Monitoring of Apple in Luochuan

Drought monitoring for apple is essential and rarely reported. Furthermore， most of studies on apple drought monitoring are based on station observations， which cannot adequately represent the spatial information. Remote sensing based drought indices can be used for spatial and temporal dynamic drought monitoring， but its applicability in apple remains to be researched. Based on the MODIS reflectance， land surface temperature and land cover data from 2014 to 2018， combined with soil moisture data and field survey， the consistency of the Temperature Vegetation Dryness Index（TVDI）， Normalized Difference Water Index（NDWI）， vegetation supply Water Index of apple with Soil Moisture（SM） at 10 cm were analyzed to explore the ability of remote sensing based drought indices in characterizing drought conditions. Then，the sensitive period of drought indices to SM was further researched. The results indicated that VSWI calculated by EVI （recorded as VSWI（EVI））had the best temporal and spatial consistency with SM， and its performance in drought monitoring in 2014 and 2017 were consistent with the actual drought.The correlation between VSWI（EVI），TVDI（EVI） and SM were higher than those of VSWI （NDVI） and TVDI （NDVI） respectively， which demonstrated that EVI can improve the characterization ability of VSWI and TVDI for drought. TVDI，NDWI，VSWI had a delay in response to SM. VSWI （EVI） with lag 24 days had the highest correlation with SM， while NDWI had timely response to SM. Therefore， combined with VSWI （EVI） and NDWI may be more conducive to monitoring drought of apple.In different growth stages， drought indices had different sensitivity to soil moisture， and VSWI has the most obvious sensitivity difference in different growth stages. At new Shoots 'vigorous Growing period （may to june），drought indices are more sensitive than that of budding and flowering， fruit expansion and maturity stages. The research results can provide a reference for monitoring drought of apple by remote sensing method.