Total ozone column from Indian geostationary satellite INSAT-3DR: Optimal infrared retrieval and validation

The multispectral infrared sounder onboard INSAT-3DR provides hourly total column ozone (TOC) retrievals at fine spatial resolution over the Indian region, alongside vertical profiles of temperature and humidity. This study presents a novel, coherent optimal algorithm for TOC retrieval from INSAT-3DR, incorporating enhanced radiance bias correction and improved a priori information. INSAT-3DR effectively captures seasonal and latitudinal TOC variations, showing strong agreement with independent satellite and ground-based observations. Statistical comparisons with TROPOMI and IASI demonstrate high concurrence, with coefficients of determination of 0.92 and 0.79, mean absolute errors of 9.34 DU and 11.47 DU, and biases of 8.65 DU and 9.90 DU, respectively. Over Delhi, INSAT-3DR TOC shows a 9.5 DU overestimation relative to Dobson measurements, with a statistically significant correlation of 0.79, comparable to TROPOMI (0.75) and IASI (0.79). Ozone profiles retrieved from INSAT-3DR and IASI are further evaluated across defined atmospheric layers, revealing higher agreement in the 600-200 hPa region where retrieval sensitivity is strongest. The tropical Indian region's complex chemical, dynamical, and geographical conditions present challenges for ozone variability, yet INSAT-3DR demonstrates strong potential for continuous monitoring and long-term ozone observations. This capability, in conjunction with meteorological parameters, can enhance understanding of atmospheric circulation, improve numerical weather prediction, and support climate change studies.