Introduction

In this section we consider the ways in which optical wavelength sensors may be characterised and provided with a calibration which is traceable to a recognised international standard. In order to be useful for long-term monitoring and repeated surveys, the calibration must also be maintained through time which implies some form of in-flight or post-launch calibration.

In addition to direct radiometric calibration, this section describes the process of 'vicarious calibration' in which the initial laboratory-based calibration is validated by an independent method, often involving terrestrial or other planetary targets.