SeaHawk/HawkEye ▸ On-Orbit Calibration

HawkEye On-Orbit Calibration

Radiometric Calibration

The HawyEye instrument consists of four CCD arrays with two bandpass filters per array to provide the 8 spectral bands for the sensor. Each band consists of an 1800 illuminated elements

Each scene includes the collection of 64 dark scans at the end of the imaging sequence. These dark scans are used to provide the electronic baseline

Calibration Equation $$L = K1[band] * DN * K2[band,pixel,time] * K3[band,temperature] * K4[band,pixel] * (1+K5[band,pixel]*DN) * K7[band,pixel]$$ where:
  • DN = Digital Number from the
  • K1 = Gain coefficients (at nadir pixel)
  • K2 = Temporal correction coefficients
  • K3 = Temperature correction coefficients
  • K4 = Response vs Scan correction coefficients
  • K5 = Non-linearity correction coefficients
  • K7 = CCD smile correction coefficients (not currently used)

Vicarious Calibration

The vicarious calibration of HawkEye was accomplished using a process similar to that used for OCTS. A clear-water radiance model based on a climatological chlorophyll time-series of SeaWiFS data over the MOBY location was used to derive an estimate of the target water-leaving radiance. MOBY data were not availble for the few dates that HawkEye imaged the MOBY location.

Geometric Registration

Since there are four separate CCDs, each supportig two spectral bands, the data from each band are offset in both the along track and cross track directions and must be registered to a common reference band. Additionally, the focal length varies slightly from band to band. Corrections for the physical offsets and the focal length differences are necessary to ensure that the data from each pixel for each band match the same geolocated area in the scene.