Calibration of INSAT-3D Meteorological Satellite Imager Using the Moon Shailesh Parihar, A.K. Mitra, A.K. Sharma Ministry of Earth Sciences India Meteorological Department, New Delhi Coordination Group on Meteorological Satellites-44

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 )

 For meteorological observations, INSAT- 3D carries a multi-spectral Imager (radiometer) capable of generating the images of the earth in six wavelength bands significant for meteorological observations, namely, visible, shortwave infrared, middle infrared, water vapor and two bands in thermal infrared regions.  The Imager generates images of the earth disk from geostationary altitude of 36,000 km every 26 minutes and provides information on various parameters, namely, outgoing long-wave radiation, quantitative precipitation estimation, sea surface temperature, snow cover, cloud motion winds, etc. Imager

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 also carries a newly developed 19 channel sounder, which is the first such payload to be flown on an ISRO satellite mission.  The Sounder has eighteen narrow spectral channels in shortwave infrared, middle infrared and long wave infrared regions and one channel in the visible region.  It provides information on the vertical profiles of temperature, humidity and integrated ozone. These profiles are available for every 30X30 kms over a selected region over Indian landmass every one hour and for the entire Indian Ocean Region every six hours. Atmospheric Sounder

INSAT-3D Sounder Channels Characteristics Detector Ch. No. c (  m) c (cm -1 ) NE  Principal absorbing gas Purpose Long wave CO 2 Stratosphere temperature CO 2 Tropopause temperature CO 2 Upper-level temperature CO 2 Mid-level temperature CO 2 Low-level temperature water vaporTotal precipitable water water vaporSurface temp., moisture Mid wave windowSurface temperature ozoneTotal ozone water vaporLow-level moisture water vaporMid-level moisture water vaporUpper-level moisture Short wave N2ON2OLow-level temperature N2ON2OMid-level temperature CO 2 Upper-level temperature CO 2 Boundary-level temp windowSurface temperature windowSurface temp., moisture Visible visibleCloud

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 insolation, surface albedo, aerosol optical depth, and cloud optical properties.

Calibration and Validation  According to Committee on Earth Observation Satellite (CEOS), calibration is the process of quantitatively defining the system response to known, controlled signal inputs and validation is the process of assessing by independent means the quality of the data products derived from the system outputs. 1. Vicarious Calibration: Reflectance-based method 2. Lunar Calibration: The sensor is pointed at the moon and allowed to scan over its surface. The total integrated radiance of the moon is then determined by summing pixels over the face of the moon and into space until the signal counts are zero.

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.  INSAT-3D measurements of lunar surface are 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.

Example of an image: how does the Moon look like?

Contd… 13 Jan, 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).  ROLO Model (GIRO) model has been installed at NSMC, IMDPS, IMD New Delhi. The version of GIRO model is GIRO_v1.0.0 and has been downloaded from

Lunar Calibration Approach: Irradiance of the Moon  Identification of lunar pixels by including all pixels with a specified number of standard deviations outward from the mean of the centrally selected area.  Get the weighted sum of radiance from the histogram of selected lunar pixels  Convert radiance (L) to irradiance (I) as  The radiances observed by INSAT-3D are integrated over the lunar imagette. We can convert disk-equivalent lunar radiance to Irradiance as given below E=L*Ω  where L is an individual radiance measurement (i.e. pixel) on the Moon, Ω is the solid angle of one pixel in the scan-corrected image.

Methodology 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 generate 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

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 (INSAT-3D) ( )W/m2/um Irradiance from GIRO model ( )W/m2/um Spectral Response Function of INSAT-3D for visible band only, the central wavelength is 0.65um.

Time Series of Irradiance Observed by INSAT-3D and GIRO model

Conclusion  The GIRO (ROLO) model output irradiance is found to be 15-20% higher with INSAT-3D observed irradiance based on 4 days observation.  This study demonstrates the capability for calibration of INSAT-3D imager using 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.

Acknowledgements Our Special thanks to: Masaya Takahashi (JMA) and Sebastien Wagner (EUMETSAT) for GIRO model and netCDF related support and GSICS members for their support regarding INSAT-3D lunar calibration.

Thank You.. Thanks for your kind attention. Suggestions and feedbacks are welcome.