Document Type : Research Article
Department of Geography, Faculty of Literature and Humanities, Lorestan University
The Visible Infrared Imaging Radiometer Array (VIIRS) is one of the key instruments on the US National Aeronautics and Space Administration's National Polar Orbiting Spacecraft (Suomi NPP), which was successfully launched on October 28, 2011, a new generation of operational intermediate-resolution imaging capabilities following NOAA's AVHRR. Enables MODIS on Terra and Aqua satellites. VIIRS covers operational environmental monitoring and numerical weather prediction with 22 radiometric imaging bands with wavelengths from 0.41 to 12.5 µm. In order to reveal the impact of precipitation on the vegetation of Lorestan province, the monthly average of the Standard Precipitation Index (SPI) was calculated using the precipitation data of 7 meteorological stations of the province. Then, using infrared images as a weekly average in the period of 2013-2021 (April 1st to the end of July) obtained from the Suomi NPP sensor, the condition of vegetation was investigated. The results showed that the correlation of standard precipitation index with (NDVI), (VCI), (TCI) and (VHI) index is 0.0037, 0.0048, 0.174 and 0.150 respectively. (TCI) has a higher correlation with (SPI), which is suitable as a combined method of remote sensing and weather station information to investigate vegetation conditions in Lorestan province. Vegetation is faced with different degrees of drought all year round, and the most severe vegetation drought occurred in 2021 in most areas of the province, especially in the central, southern and northeastern parts of the province. In 2013, 2015, and 2018, vegetation drought occurred with less severity, and in 2016, 2018, 2019, and 2020, vegetation was in more favorable conditions.