Introducing a Modificated Local Model of MODIS with Respect to Radiosonde Data, and Estimation of LWIR Radiation Transmission

Aims: Using a latitude dependent local corrected model and based on MODIS data around Mehrabad Synoptic Station of Tehran, the spectral radiance in long wavelength infrared region was modeled and calculated for total upward and downward radiation flux and direct downward radiation flux for cold and hot seasons.

Study Design: Design of the study includes the calculations of local atmospheric profile of the subjected region by radiosonde data, calculations of the atmospheric profile by MODIS data for same region. It presents a latitude dependent relation for modifying the MODIS data of any point which properly could be used instead of radiosonde data at that point and finally model and calculate LWIR’s total emitted flux at different heights for the area around subjected region with local profile for both hot (June, July, August) and cold (January, February, March) seasons.[G7] [G8]

Place and Duration of Study: Department of Optic and Laser, Faculty of science, I. H.U University, between February 2016 and December 2017.

Methodology: The radiosonde and MODIS raw data of 13 stations with different latitudes in 1995-2015 were used for modification purpose. By applying statistic calculations on raw data, the atmospheric profile was extracted. Radiosonde data were not available in any points of a region, while the MODIS data were available. A latitude dependent relation is presented in this work for modifying the MODIS data of any point which properly could be used instead of radiosonde data at that point.

Results: The results were compared and assessed with the default profiles of sub-arctic winter and tropical models. The RMSEs for total upward, downward, and direct radiation fluxes in terms of wavelength in long wavelength infrared in cold and hot seasons were 2.45 Wm-2µ-1 and 1.722 Wm-2µ-1, respectively.

Conclusion: The results showed that local atmospheric profile plays a key role in modifying atmospheric effects on TIR hyperspectral radiance and their accurate understanding improves the quality and quantity of the radiances reaching a sensor and helps better detection of the spectral signature of the study objectives.