INSAT-3D Calibration Using Moon at IMD A.K. Mitra, Shailesh Parihar, S.K Peshin A.K. Sharma Ministry of Earth Sciences India Meteorological Department, New Delhi

Brief History of INSAT Satellites  Satellite Meteorology in IMD started in 1982 with the launch of INSAT-1A which was a multipurpose satellite meant for services to Meteorology, Doordarshan and Communication. Before that, Indian meteorologists were using analog imageries received from U.S. Polar orbiting satellites series of TIROS-N. INSAT-1A – 10 April 1982 Two Channel VHRR INSAT-1B – 30 August,1983 INSAT-1C – 21 July 1988 INSAT-1D – 12 June,1990 INSAT-2A – 10 July, 1992 INSAT-2B – 23 July,1993 INSAT-2E – 03 April 1999, KALPANA-1 – 12 Sept.2002, INSAT-3A – 10 April 2003 have Three Channel VHRR INSAT-3D – 26 July, channel imager and 19 channel sounder

Kalpana-1 INSAT-3D:2013 INSAT-3A 74 o 82 o 93.5 o Current Indian Geostationary Meteorological Satellites

INSAT-3D - India’s Advanced Weather Satellite India's advanced weather satellite INSAT-3D was launched in the early hours of July 26, 2013 from Kourou, French Guyana, and has successfully been placed in Geosynchronous orbit. It carries four payloads  Imager (Six Channels)  Sounder (Nineteen Channels)  Data Relay Transponder(DRT)  Satellite Aided Search and Rescue (SAS & R )

INSAT 3D satellite Imager Channel Spectral BandWave-length(µm)Ground Resolution Visible km SWIR km MIR km WV km TIR km TIR km

INSAT-3D Spectral Response Function The Earth’s surface and clouds have been observed for many years by meteorological satellites operating in geostationary Earth orbit (GEO), distributed in longitude around the globe. Images from solar-band channels (visible and shortwave infrared, 0.4–2.5 μm) have been used to monitor important climate variables such as surface insulation, surface albedo, aerosol optical depth, and cloud optical properties.

The Moon in INSAT-3D images  In INSAT-3D satellite the Moon appears regularly in full-disk operational images of the Earth acquired by meteorological instruments with a rectangular field of regard, several times each month, which provides an excellent opportunity for radiometric calibration.  The Moon is being observed from INSAT-3D regularly in the of full-disk operational image of earth with rectangular field of regard in IMDPS New Delhi.  INSAT-3D measurements of lunar surface observed in Visible ( µm), Short Wave Infrared µm, Mid Wave Infrared ( µm), Water Vapor (WV) µm, Thermal Infrared (TIR) 1 & 2, µm & µm wavelength regions.  The visible and infrared wavelengths region provide a new and intriguing methodology of distinguish in sensitivities of Earth observing radiometers.

INSAT-3D visible channel full-disk image acquired 2015 July 05. The Moon is captured in southwest corner on 0859 UTC.

Moon Images in INSAT-3D 27 Oct, UTC in VIS 27 Oct, UTC in VIS

GSICS Implementation of ROLO Model: GIRO  The USGS RObotic Lunar Observatory (ROLO) project has developed the capability for on-orbit calibration using the Moon via a GSICS (Global Space based Inter calibration System) Implementation of ROLO Model (GIRO)  Lunar spectral irradiance that accommodates the geometries of illumination and viewing by a spacecraft. ROLO model is work on lunar spectral irradiance that accounts for phase and libration explicitly.  ROLO Model (GIRO) model has provided by the EUMETSAT and installed at IMDPS, IMD New Delhi. The version of GIRO model GIRO_v1.0.0 has been downloaded from

Methodology at IMD Find the Moon in INSAT-3D full frame image and then collect L1B data and decode VIS and SWIR channels Consider only lunar pixels for specific channels and make template.ncl file Input template.ncl file to generates netCDF file by ncgen utility.nc file is the input format of GIRO model, Run that model and get output files Compare the results of irradiance of GIRO model and INSAT-3D satellite lunar imagette irradiance and other scientific analysis Generate calibration coefficients This template.ncl file having information of OSF, Satellite Cartesian Coordinates, Pixel Solid Angle, Time & date of satellite image at the time of Moon acquired, Satellite Position References, Spectral lunar pixel radiance converted to irradiance and Spectral Response Function of INSAT-3D

Step by step method for GIRO input  First, Identification of lunar pixels and calculate the sum of the lunar pixels (which included digital counts and radiances)  Make template.ncl file for lunar pixels, it is input for generates netCDF file.  Radiances observed of lunar pixels are converted to the irradiance, this is input of GIRO model.  Lunar data (irradiance) converted to netCDF using IDL code with Compulsory inputs: 1.Lunar observation imagette time(hour, minute, second), Date (year, month, date) 2.Satellite Position References 3.Satellite Cartesian Coordinates at the time of Moon acquired 4.Over Sampling Factor 5.DC observations

From these processes and ephemeris calculations for the Moon and INSAT- 3D, the following values were found for visible channel only: Over Sampling Factor IFOV28 μrad Pixel Solid Angle steradian Scan Rate20 o /sec + 0.2sec turn around Nominal Altitude36000 km (GEO) Satellite Position ReferencesJ2000 Lunar observation time(hr, min, sec)& Date (year, month, date)-- Satellite Cartesian Coordinates , , Irradiance Observation of Moon ( )W/m2/um Irradiance GIRO ( )W/m2/um Spectral Response Function of INSAT-3D for visible band only, the central wavelength is 0.65um.

Time Series of Irradiance Observed INSAT-3D and GIRO

Conclusion  Although, this is four days observation comparison and the result is consistent with INSAT-3D visible-channel underestimate over time period.  The GIRO (ROLO) model output irradiance is found to be 15-20% higher with INSAT-3D observed irradiance.  This study demonstrates the capability for calibration of INSAT-3D imager that has viewed the Moon.  However, conformity of result requires a long time observation of INSAT- 3D lunar images to compare with GIRO model irradiance for better precision levels.

My Special thanks to:  Sebastien Wagner (EUMETSAT) for providing the Software and helping us to installed at IMD.  Masaya Takahashi (JMA, Japan) for operate understand GIRO model netCDF related support and GSICS members for his support regarding INSAT-3D lunar calibration.  DGM, IMD for constantly supporting the work and providing all the facilities to carried out this work.  Satish R Kulkarni, Master Control Facility, Hassan, ISRO for providing the support.

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