Study the variability of surface temperature and chlorophyll concentration in rice fields: a case study in southern region of Sri Lanka

Abstract

Measuring the chlorophyll content of a plant is generally done by using laboratory techniques and field testing equipment. Modern remote sensing approaches have a potential to identify the correct quantity of chlorophyll in the fields. There are many plant indicess that have been developed for measuring leaf chlorophyll content. Traditional approaches of measuring leaf chlorophyll may incur high costs and can be time consuming in large fields. Hambantota district is considered as a large-scale paddy cultivating area. Paddy lands from Ranna, Hungama and Angunukolapelessa cities were selected for this analysis. Drone images, Landsat 8 satellite images were collected from each field corresponding to field sampling dates. Paddy leaf samples were collected to measure the actual chlorophyll content. Laboratory acetone extraction method was used to estimate the actual chlorophyll and ArcGIS software was used to develop the normalized difference vegetation index (NDVI) maps, Visible atmospherically resistant index (VARI) maps and land surface temperature (LST) maps of the three selected paddy fields. Chlorophyll content calculated from the satellite images and drone images was compared with actual laboratory leaf chlorophyll content to build an index and to find the correlation between them. It was possible to identify a positive correlation (R2= 0.7268) between NDVI and the plant chlorophyll content. It was observed that the LST maps and NDVI maps developed graphycally show inverse relationships. In addition, VARI maps can be used similarly as NDVI maps to estimate the chlorophyll content of the paddy leaves. Instead of satellite images, low cost drones which have no near infrared spectroscopy (NIR) sensors are suitable for measuring the plant chlorophyll content using the VARI.Therefore, more investigations should be done on the applications of drone and satellite images as a non - destructive method to estimate the chlorophyll content of paddy leaves.