IEEE Geoscience and Remote Sensing Magazine - June 2015 - 28

quality information, the IPS is maintained by the CQC, its
format is entirely described with an xml schema descriptor. This approach is convenient for requesting specification accuracy, unit and description in order to facilitate
analyzing specifications across missions.
Hence, a specific visualization / analysis tool has been
created in order to monitor, add comments to a given IPS
parameter and furthermore inter compare parameters. The
analysis tool is open to the community [17].
Table 2 lists the IPS parameters for an optical system that
have been considered as a priority for being harmonized
across the data provider. In this context, the harmonization
of IPS parameters addresses two main topics; the system of
units and the methods used to derive the parameters. To
adopt a single system of units is the first stage for being able
to compare parameters, however it is not sufficient. A dis-

cussion on how parameters have been harmonized is given
in the next section of this publication (E).
During the last three years, the IPS parameters have
been investigated and monitored. As shown in Table 2, besides the name of the IVOS, it is interesting to observe that
there is a proposed parameter system and a description of
the parameters. For different missions, it is unfortunately
rare to have a parameter expressed by the same measure
and obtained by using the same method. The CQC has
proposed transformation rules, in agreement with the data
provider to put values into the same scale and therefore to
allow inter-comparison.
The quality information strictly related to the instrument and product is complemented with the Copernicus
dataset specifications [13]. These latter specifications
address each dataset and deal with acquisition window,

table 2. tHe lISt Of Infrared/VISIble OptIcal SYStemS (IVOS) parameterS and tHeIr defInItIOn, tHeY are
InclUded IntO tHe InStrUment and prOdUct SpecIfIcatIOn dOcUment Of an OptIcal SYStem.
IVOS IdentIfIer

name

deScrIptIOn

IVOS-04

Ground Sample/ing Distance (GSD) [m]

Ground Sample Distance (GSD) refers to the size of the pixels expressed in
ground units. The pixel size has not to be confused with the spatial resolution
which instead identifies the minimum separation between two objects at
which the resulting images of the objects appear distinct and separate.

IVOS-05 / 06

Modulation Transfer Function (MTF) at
Nyquist frequency

The Modulation Transfer Function describes the response of the imaging sensor as a function of the spatial frequency. The MTF value shall be specified at
a spatial frequency equal to the Nyquist frequency (half the focal plane image
sampling frequency).

MTF calculation procedure

IVOS-07

Effective Isotropic Field-Of-View (EIFOV)

This is defined as the ground resolution corresponding to a spatial frequency
for which the system MTF is 50%. In case of differences between EIFOV computed along and across track, the geometric mean is provided.

IVOS-08

Radiometrically accurate IFOV [value at
specific frequency]

IVOS-09

Band to band registration [DRMS at 1
sigma]

Distortions and differences between the various instrument's bands due
to the detector (e.g. focal plane alignment and stability). The multi-spectral
registration is the quadratic average distance between the pixel centers of
each multi-spectral band corresponding to a selectable point. This error is
measured relatively from a reference band to the others bands.

IVOS-10

Centring accuracy [DRMS at 1 sigma]

Centring accuracy is associated with the programming function and concerns
the ability of the system to optimally point a target on ground. This is the
difference between a theoretical centre of an image at the programming step
and his real position in the acquired image.

IVOS-11

Direct geo-location accuracy [DRMS at
1 sigma]

The location error stands for the deviation between the real position of any
point on an image and its estimated position using the ancillary data of the
product without ground control points.

IVOS-12

Geo-location accuracy for orthorectified
products [DRMS at 1 sigma]

The location error after orthorectificaiton represents the deviation between
the estimated coordinates and elevation of any point on an image and its real
position and elevation on the ground.

IVOS-13

Orthorectification procedure

Description of the applied orthorectification procedure specifying the algorithm, sensor model, used Digital Elevation Model (DEM) or Digital Terrain
Model (DTM), used ground control points, or reference images.

IVOS-20

Absolute Calibration

Relationship between quantity values provided by measurement standards
and the corresponding indications of a measuring system, carried out under
specified conditions and including evaluation of measurement uncertainty.
The absolute calibration is determined by the coefficients needed to transform
the acquired data into values obtained via accurate ground reference measurements and taking into account all system's errors. A different set of coefficients is used for each spectral band.

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Table of Contents for the Digital Edition of IEEE Geoscience and Remote Sensing Magazine - June 2015