How do you calibrate the optical sensor on each satellite?

We undertake the following calibrations on our Dove satellites:

• Sensor Calibration: calibration of known parameters that are specific to each satellite sensor and optical assembly, such as flat field correction, de-noising, bad column adjustment (fixing anomalies based on known sensor defects), optical aberration correction and balancing CCD columns.
  
  
• Photometric Calibration: images are adjusted to a nominal brightness configuration and color profile to ensure overall product consistency, including adjustments for differences in exposure technique, count, exposure time, gain and sun angle.
  
  
• Radiometric Calibration: calibration of each sensor is established and maintained using a combination of pre-launch and on-orbit radiometric calibration techniques. On-orbit techniques include lunar calibration and cross-calibration with well calibrated satellites (such as RapidEye). Calibration coefficients are regularly updated in order to maintain high per-satellite radiometric accuracy across time and ensure low inter-satellite uncertainty.

We are also working on more advanced forms of radiometric calibration.