Accuracy : Closeness of the agreement between the result of a measurement
and a true value of the measurand.
Atmospheric correction : The process of removing the effect of the atmosphere on a signal recorded by an aircraft or satellite sensor. In optical wavelength remote sensing this is usually taken to include removal of the effects of absorption and scattering by gas molecules and aerosols but not the removal of clouds and cloud shadows (see cloud-screening below).
AtmChem: Atmospheric Chemistry (CEOS subgroup).
Calibration: The process of quantitatively defining the system responses to known, controlled signal inputs.
CEOS: Committee on Earth Observation Satellites.
CEOP: Coordinated Enhanced Observation Period.
Cloud-screening : The identification and possible removal of clouds and related features such as cloud shadows from remotely sensed data.
Error : Difference between the result of a measurement and the true value of the measurand.
Precision : This term is best avoided in metrological applications because it is ambiguous and better terms are available (see below). In general terms, 'precision' equates to 'repeatability'.
GOFC: Global Observation of Forest Cover.
Goniometer : A device to enable an instrument to be moved through a range of view zenith angles relative to a target surface. Most goniometers also have means to adjust the view azimuth angle, thereby allowing the directional properties of the surface to be measured. The term 'goniospectroradiometer' or 'spectrogoniometer' is sometimes used to describe the combination of a goniometer and a spectroradiometer.
IGOS: Integrated Global Observing Strategy.
ISPRS: The International Society for Photogrammetry and Remote Sensing.
IVOS: Infrared and visible optical sensors (CEOS subgroup).
LPV: Land Product Validation (CEOS subgroup).
MSSG: Microwave sensors (CEOS subgroup).
Radiative transfer model : A mathematical description of the propagation of electromagnetic radiation through the atmosphere. A radiative transfer model may be designed to predict the top-of-atmosphere (TOA) spectral radiance from measurements made at ground level, in which case it will be necessary to invert the model when using satellite data as we are interested in estimating the ground-leaving radiance from TOA measurements.
Repeatability : Closeness of the agreement between the results of successive measurements of the same measurand carried out under the same conditions of measurement.
Reproducibility : Closeness of the agreement between the results of measurements of the same measurand carried out under changed conditions of measurement.
SAR: Synthetic Aperture Radar (CEOS subgroup).
Stability : Ability of a measuring instrument to maintain constant its metrological characteristics with time.
Sunphotometer : a specialised multiband radiometer designed to collect data for use in characterising the properties of the atmosphere. This is done by measuring the spectral properties of the solar disc and other parts of the sky. Sunphotometers must have a very narrow and well-defined field-of-view, stable radiometric properties, wide dynamic range, and some means of pointing them very accurately.
TOA : Top of the atmosphere.
TM : Terrain Mapping (CEOS subgroup).
Traceability : Property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually through an unbroken chain of comparisons, all having stated uncertainties.
Uncertainty : A parameter associated with the result of a measurement that characterises the dispersion of values that could reasonably be attributed to the measurand.
Validation: The process of assessing, by independent means, the quality of the data products derived from the system outputs.
Vicarious Calibration : This term refers to the in-flight or in-orbit radiometric calibration of an aircraft or satellite sensor by a method independent of that used to perform the initial laboratory calibration. Two methods are commonly used : the radiance-based method in which data from the sensor are compared with radiance measured by a highly accurate sensor mounted on an aircraft, and the reflectance-based method in which a radiative transfer model is used to estimate the top-of-atmosphere radiance from a ground target of known reflectance.
WGCV: Working Group on Calibration & Validation.
Fox, N.P., 2001, Traceability to SI for EO measurements. CEOS WGCV Cal/Val Newsletter 9, January 2001, 1-9.
Slater, P.N. et al. (1987) Reflectance- and radiance-based methods for the in-flight absolute calibration of multispectral sensors. Remote Sensing of Environment, 22, 11-37.