Kamal Omidvar; massumeh nabavi zadeh; Ahmad Mazidi; HamidReza Ghaffarian Malmiri; Peyman Mahmoudi
Abstract
Drought monitoring is critical for early warning of drought hazard. This study is attempted to develop remote sensing drought monitoring index (VDI), based on Accuracy of different bands of Moderate Resolution Imaging Spectroradiometer data MODIS, VDI focuses about the vegetation water stress. Spectral ...
Read More
Drought monitoring is critical for early warning of drought hazard. This study is attempted to develop remote sensing drought monitoring index (VDI), based on Accuracy of different bands of Moderate Resolution Imaging Spectroradiometer data MODIS, VDI focuses about the vegetation water stress. Spectral studies have demonstrated that due to the large absorption by leaf water, shortwave infrared reflectance (SWIR) is negatively related to leaf water content. Being sensitive to leaf water content, SWIR is widly utilized to construct various remote-sensing indices for example VDI for reflecting vegetation water content, . In this study, Vegetation Drought Index (VDI) was evaluated Based on the sensitivity rate to moisture by shortwave infrared reflectance bands SWIR 5 and 6 (VDI5 and VDI6). The data included the MODIS sensor images from Terra satellite in a period of nineteen years from 2000 to 2018 and Precipitation data are obtained from the Global Land Data Assimilation System (GLDAS), in Sistan & Balouchestan Province, Pearson correlation coefficient was used to evaluate the accuracy of the Drought spatial distribution maps calculated based on the two bands.Results indicate high significant correlation rate between VDI6 and Precipitation data . Study also showed that shortwave infrared band 6 (SWIR) is more sensitive to agricultural drought than band 5,in Sistan and Baluchestan province . The study recommends to use VDI index with and 6 for better early detection and monitoring of agricultural drought in operational drought management programmes.
Fateme Firozi; Taghi Tavosi; Peyman Mahmoudi; Seyed Mahdi Amir Jahanshahi
Volume 10, Issue 4 , February 2019, , Pages 69-84
Abstract
The radative energy balance received and returned from Earth planet reflects the energy available in each part of the Earth-Atmosphere system. Also, net solar radiation is the most fundamental driving force for evaporation, and all actions and reactions between the Earth's surface and the atmosphere. ...
Read More
The radative energy balance received and returned from Earth planet reflects the energy available in each part of the Earth-Atmosphere system. Also, net solar radiation is the most fundamental driving force for evaporation, and all actions and reactions between the Earth's surface and the atmosphere. These reactions significantly affect the climate and its transformations. Hence, the wide-scale cross-sectional estimation of pure net energy is important in terms of global and regional climate models. In this research, in order to study the trend of long-term monthly average changes of surface-Albedo, the Albedo products from the sensors of MODIS Satellite Terra named MCD43B3were used. The spatial resolution of the images taken was 1×1 km for a 15-year statistical period (2000-2014) for April, May, and June. After capturing images by NASA's land processes distributed active archive center, all 45 downloaded images. The next step was to convert the image format to ASCII format; each ASCII includes 30080 pixels. Finally, by using both statistical methods of Sen's slope estimator, and Classic Linear Regression the trends of long-term monthly average Albedo changes were analyzed on a pixel-based scale. The results of these two models showed that these two models did not differ in their estimation of the trends of Albedo's average changes, and acted precisely the same. Also, the results of this research showed that the center of the most slowly declining slope of Albedo changes is located in the northeast, where, due to the flow of the Hirmand River, in this part of the plain the agriculture is widespread. The incremental magnitude of the slope of the change process is also very limited, and there are small and large spots in the north, northeast, and center of the plain. This increasing trend in the values of Albedo's index in the north of the plain was exactly the same as the drying of the Hamoon triple lakes. The rest of the plain area, which has desert landscape and does not have any vegetation, as well as any human population, has not shown any particular trend. In this study, it was also clearly found that, the use of nonparametric method of Sen's slope estimator and parametric method of classic linear regression can be very effective in studying the trend of Albedo changes in the arid regions resulted from satellite products of MADIS sensors
