# FIDUCEO Vocabulary

This is the FIDUCEO draft vocabulary. We encourage comments on our definitions, please click on any word to comment.

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### Random

Random errors are errors manifesting independence: the error in one instance of a quantity is in no way predictable from knowledge of the error in another instance: the error in each instance is considered to be an independent draw from an underlying probability distribution; “random” implies in this context both “unpredictable” and “uncorrelated between measured values” (within a given processing level); random errors therefore tend to “average out” across many measured values, and the uncertainty in the average of the measured values decreases with more measurements; random effects may be operating at the same time as other types of effect, in which case only a component of the total error is random; an example of a random effect (an effect giving rise to random errors) is electronic noise in an amplifier circuit.

A complication arises in a chain of processing in which a quantity subject to random errors at a one level then influences many values in a higher level of processing: the originating effect may be random (or, “aleatoric”) but at the higher level the resulting errors across many values are not independent. For this reason, we use “random” to discuss the nature of an effect, and “independent” to signify “uncorrelated across measured values”.

### Random effects

Random effects are those causing errors that cannot be corrected for in a single measured value, even in principle, because the effect is operates by chance, i.e., is aleatoric. Random effects for a particular measurement process vary unpredictably from (one set of) measured values(s) to (another set of) measured values(s), and produce random errors in those measured values.

### Re-gridding

This term refers to the process of transforming the information represented in one grid into another grid.

### Re-projection

This term refers to the process of transforming the information represented in one type of projection into another type of projection.

### Recalibration

A recalibrated dataset is one where the calibration coefficients and/or the calibration algorithm has been updated relative to the operational calibration used to create the original satellite Level 1 datasets. The operational calibration is normally derived from pre-launch measurements and there are many instances where the pre-launch data/algorithm is insufficient to calibrate the sensor in orbit either due to changes in the satellite response while in orbit or due to problems with the pre-launch data/algorithm itself or both.

### Relative uncertainty

An uncertainty given in relative units (per cent, parts per million, fractions, etc). This is generally written u(xi)/xi