Definitions

Click one of the letters above to advance the page to terms beginning with that letter.

A

accuracy

closeness of agreement between a measured quantity value and a true quantity value of a measurand. Note that it is not a quantity and it is not given a numerical quantity value. A measurement is said to be more accurate when it offers a smaller measurement error.

area (volume) of representativeness

the area (volume) in which the concentration does not differ from the concentration at the station by more than a specific range

audit

systematic, independent and document process for obtaining objective evidence and evaluating it objectively to determine the extent to which the audit criteria are fulfilled

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B

bias

(1) systematic error of indication of a measuring system
(2) estimate of a systematic measurement error
(3) estimate of a systematic forecast error

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C

calibration

(1) the process of quantitatively defining the system responses to known, controlled signal inputs
(2) operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication

climate data record (CDR)

a time series of measurements of sufficient length, consistency and continuity to determine climate variability and change

correction

compensation for an estimated systematic effect. Note: The compensation can take different forms, such as an addend or a factor, or can be deduced from a table.

coverage probability

probability that the set of true quantity values of a measurand is contained within a specified coverage interval

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D

dead band (or neutral zone)

maximum interval through which a value of a quantity being measured can be changed in both directions without producing a detectable change in the corresponding indication

detection limit

measured quantity value, obtained by a given measurement procedure, for which the probability of falsely claiming the absence of a component is β, given a probability α of falsely claiming its presence

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E

error

(1) measured quantity value minus a reference quantity value
(2) difference of quantity value obtained by measurement and true value of the measurand
(3) difference of forecast value and a, estimate of the true value
Note: (1) and (2) refer to measurement error, while (3) refers to a forecast error

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F

fiducial

used as a fixed standard of reference for comparison or measurement (fiducial point)

fiducial mark

index mark on a test system that allows automatic geometric identification and orientation detection of an object using imaging systems

fiducial reference measurement

the suite of independent ground measurements that deliver, for a satellite mission, and to users, the required confidence in data products, in the form of independent validation results and satellite measurement uncertainty estimation, over the entire end-to-end duration of a satellite mission

field-of-regard

an area of the object space scanned by the field-of-view of a scanning sensor

field-of-view

the solid angle from which the detector receives radiation

footprint

the area of a target encircled by the field-of-view of a detector of radiation, or irradiated by an active system

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G

geometrical resolution

ability of a sensor system to record signals separately from neighboring object structures

ground sampling distance (GSD)

linear distance between pixel centres on the ground

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I

in situ measurement

(1) a direct measurement of the measurand in its original place
(2) any sub-orbital measurement of the measurand

indication

quantity value provided by a measuring instrument or a measuring system

influence quantity

quantity that, in a direct measurement, does not affect the quantity that is actually measured, but affects the relation between the indication and the measurement result

instantaneous field of view (IFOV)

opening angle corresponding to one detector element

instrumental drift

continuous or incremental change over time in indication, due to changes in metrological properties of a measuring instrument. Note that instrumental drift is related neither to a change in a quantity being measured nor to a change of any recognized influence quantity.

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L

Level 0 data

reconstructed, unprocessed instrument and payload data at full resolution, with any and all measurement and communications artifacts removed

Level 1a data

reconstructed, unprocessed data at full resolution, time referenced, and annotated with ancillary information, including radiometric and geometric calibration coefficients and geo-referencing parameters (e.g., ephemeris) computed and appended but not applied to the Level 0 data

Level 1b data

calibrated, geo-located Earth reflectance and radiance spectra in all spectral bands; solar irradiance data, annotation data and references to used calibration data

Level 2 data

geophysical measurand at the same resolution and geolocation as the Level 1 source data from which it is derived

Level 3 data

data or retrieved geophysical parameters (i.e. derived from Level 1 or 2 data products) mapped on uniform space-time grid scales, usually with some completeness and consistency. Such re-sampling may include averaging, compositing, kriging, use of Kalman filters…

Level 4 data

model output or results from analyses of lower level data, i.e., parameters that are not directly measured by the instruments, but are derived from these measurements

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M

measurand

quantity intended to be measured

measurement covariance matrix

symmetric positive semi-definite matrix of dimension N × N associated with an estimate of a real vector quantity of dimension N × 1, containing on its diagonal the squares of the standard uncertainties associated with the respective components of the estimate of the quantity, and, in its off-diagonal positions, the covariances associated with pairs of components of that estimate

metadata

data about the data; parameters that describe, characterise, and/or index the data

monitoring

(1) systematic evaluation over time of some quantity
(2) by extension, evaluation over time of the performance of a system, of the occurrence of an event etc.

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P

point-to-area (point-to-volume) representativeness

the probability that a point measurement lies within a specific range of area-average (volume-average) concentration value

positional accuracy

closeness of coordinate value to the true or accepted value in a specified reference system

precision

(1) measure of the repeatability of a set of measurements. Note that precision is usually expressed as a statistical value based upon a set of repeated measurements such as the standard deviation from the sample mean (2) closeness of agreement between indications or measured quantity values obtained by replicate measurements on the same or similar objects under specified conditions

procedure

specified way to carry out an activity or a process

process

set of interrelated or interacting activities that use inputs to deliver an intended result

process validation

establishing documented evidence of a high degree of assurance that a specific process will consistently produce a product meeting its pre-determined specifications and quality characteristics

product

output of an organization that can be produced without any transaction taking place between the organization and the customer

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Q

quality

the totality of features and characteristics of a product or service that bears its ability to satisfy stated or implied needs

quality assessment

term referring to the derivation of quality indicators providing sufficient information to assess whether quality requirements are fulfilled

quality assurance (QA)

part of quality management focused on providing confidence that quality requirements will be fulfilled; it is different from quality assessment and from quality control

quality control (QC)

(1) QC refers to the activities undertaken to check and optimise accuracy and precision of the data after its collection
(2) part of quality management focused on fulfilling quality requirements

quality indicator (QI)

a means of providing a user of data or derived product with sufficient information to assess its suitability for a particular application. This information should be based on a quantitative assessment of its traceability to an agreed reference or measurement standard (ideally SI), but can be presented as a numeric or a text descriptor, provided the quantitative linkage is defined.

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R

radiometric calibration

a determination of radiometric instrument performance in the spatial, spectral, and temporal domains in a series of measurements, in which its output is related to the true value of the measured radiometric quantity

random error

(1) component of measurement error that in replicate measurements varies in an unpredictable manner; note that random measurement error equals measurement error minus systematic measurement error.
Note: Random measurement errors of a set of replicate measurements form a distribution that can be summarized by its expectation, which is generally assumed to be zero, and its variance.
(2) component of forecast error that varies in an unpredictable manner

relative standard uncertainty

standard measurement uncertainty divided by the absolute value of the measured quantity value

repeatability

measurement precision under set of conditions including the same measurement procedure, same operator, same measuring system, same operating conditions and same location, and replicated measurements over a short period of time

representativeness

the extent to which a set of measurements taken in a given space-time domain reflect the actual conditions in the same or different space-time domain taken on a scale appropriate for a specific application

reproducibility

measurement precision under a set of conditions including different locations, operators, and measuring systems

resolution

(1) smallest change in a quantity being measured that causes a perceptible change in the corresponding indication
(2) the least angular/linear/temporal/spectral distance between two identical point sources of radiation that can be distinguished according to a given criterion
(3) the least vertical/geographical/temporal distance between two identical atmospheric features that can be distinguished in a gridded numerical product or in time series of measurements; resolution is equal to or coarser than vertical/geographical/temporal sampling of the grid or the measurement time series

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S

sensitivity of a measuring system

quotient of the change in an indication of a measuring system and the corresponding change in a value of a quantity being measured. Note: sensitivity can depend on the value of the quantity being measured. The change considered in a value of a quantity being measured must be large compared with the resolution.

service

output of an organization with at least one activity necessarily performed between the organization and the customer

stability

Property of a measuring instrument, whereby its metrological properties remain constant in time

standard uncertainty

measurement uncertainty expressed as a standard deviation

system

set of interrelated or interacting elements

systematic error

component of measurement error that in replicate measurements remains constant or varies in a predictable manner
Note that systematic measurement error, and its causes, can be known or unknown. A correction can be applied to compensate for a known systematic measurement error.
(Note from GUM , 3.2.3): It is assumed that, after correction, the expectation or expected value of the error arising from a systematic effect is zero.
(Note from GUM , 3.3.1): The result of a measurement after correction for recognized systematic effects is still only an estimate of the value of the measurand because of the uncertainty arising from random effects and from imperfect correction of the result for systematic effects.

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T

traceability

(1) (metrological traceability) property of a measurement result relating the result to a stated metrological reference (free definition and not necessarily SI) through an unbroken chain of calibrations of a measuring system or comparisons, each contributing to the stated measurement uncertainty
(2) ability to trace the history, application or location of an object, a product or a service

traceability chain

sequence of measurement standards and calibrations that is used to relate a measurement result to a reference

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U

uncertainty

non-negative parameter characterizing the dispersion of the quantity values being attributed to a measurand, based on the information used

uncertainty budget

statement of a measurement uncertainty, of the components of that measurement uncertainty, and of their calculation and combination.

uncertainty of measurement method

uncertainty associated with the method of measurement, as there can be other methods, some of them as yet unknown or in some way impractical, that would give systematically different results of apparently equal validity.

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V

validation

(1) the process of assessing, by independent means, the quality of the data products derived from the system outputs
(2) verification, where the specified requirements are adequate for an intended use
(3) confirmation, through the provision of objective evidence, that the requirements for a specific intended use or application have been fulfilled
(4) the process of assessing, by independent means, the degree of correspondence between the value of the radiometric quantity derived from the output signal of a calibrated radiometric device and the actual value of this quantity.
(5) confirmation by examination and provision of objective evidence that specifications conform to user needs and intended uses, and that the particular requirements implemented through software can be consistently fulfilled

verification

(1) provision of objective evidence that a given item fulfils specified requirements; note that, when applicable, measurement uncertainty should be taken into consideration.
(2) confirmation, through the provision of objective evidence, that specified requirements have been fulfilled
(3) the provision of objective evidence that the design outputs of a particular phase of the software development life cycle meet all of the specified requirements for that phase

vicarious calibration

post-launch calibration of sensors that make use of natural or artificial sites on the surface of the Earth

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