Position and attitude determination Image acquisition request
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Validation is the process of assessing, by independent means, the quality of the data products derived from the system outputs [CEOS]
Calibration of sensor data is critical for comparison of observations over time and between sensors. Sensor data traceable to standard sources is critical to the use of observations in science-based activities. For example, UV
monitoring from space offers the opportunity to achieve global coverage of the UV radiation field. Derived information is only useful to policy makers if the underlying data are rigorously quality assured, i.e. are “of known quality and
adequate for their intended use”.
Calibration is not always critical. For small target detection in single-channel data, image calibraion is often unnecessary because there is no concern for precise measurements only the contrast between the target and its
background.
Techniques for calibration are based on metrology that establishes general rules for evaluating and expressing uncertainty in measurement. Metrology is mainly concerned with the uncertainty in the measurement of a well-defined
physical quantity - the measurand - that can be characterised by an essentially unique value. It also covers the evaluation and expression of uncertainty associated with the experiment design, measurement methods, and complex
systems.
Metrology is focused on measurable quantities. A measurable quanity is an attribute of a phenomenon, body or substance that may be distinguished qualitatively and determined quantitatively [VIM]. A measurement is a set of
operations having the object of determining a value of a quantity [VIM]. A measurand is a particular quantity subject to measurement [VIM].
A focus of calibration is to determine the accuracy of measurement. Accuracy is a qualitative concept that described the closeness of the agreement between the result of a measurement and a true value of the measurand [VIM].
Quantiatively the uncertainty of measurement characterizes the dispersion of the values that could reasonably be attributed to the measurand.
Editor’s note ISO 19113 references ISO 3534-1 for definition of accuracy which differs from VIM definition Uncertainty of measurement comprises, in general, many components. Some of these components may be evaluated
from the statistical distribution of the results of series of measurements and can be characterized by experimental standard deviations. The other components, which can also be characterized by standard deviations, are evaluated
from assumed probability distributions based on experience or other information.
It is understood that the result of the measurement is the best estimate of the value of the measurand, and that all components of uncertainty, including those arising from systematic effects, such as components associated with
corrections and reference standards, contribute to the dispersion.
For calibration, metrology defines the techniques of traceability. Traceablility is the property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international
standards, through an unbroken chain of comparisons all having stated uncertainties [VIM]
For image sensing data requiring calibration, the uncertainty of the sensor shall be measured. Determination of uncertainty for an imaging sensor traceability shall be defined.