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THE STRUCTURE OF THE APEX (AIRBORNE PRISM EXPERIMENT) PROCESSING AND
ARCHIVING FACILITY
Hueni, A.1, Bieseman J.
2, Dell’Endice, F.
1, Alberti, E.
1, Meuleman K.
2 and Schaepman M.
1
1 Remote Sensing Laboratories, Department of Geography, University of Zurich, Switzerland
2 VITO-TAP, Mol, Belgium
ABSTRACT
APEX is a Swiss-Belgian project for the realization of an
airborne imaging spectrometer within the framework of the
ESA Prodex Programme. The project’s emphasis is on
delivering products characterized by high level accuracy to
the user community. This objective relies on the concept and
the actuation of two fundamental phases: (a) instrument
calibration and (b) data processing. An accurate instrument
calibration procedure is required in order to achieve a proper
knowledge of the instrument behavior. The calibration
information is structured into calibration cubes. These
calibration cubes are then integrated into the specialized
processing for data calibration to convert the raw system
data into physical (spectral, radiometric, spatial) units.
Higher-level products can be ordered and configured by the
end users via according web interfaces. The dedicated
APEX Processing and Archiving Facility (PAF) is hosted
and operated by VITO.
Index Terms— Processing, archiving, calibration,
imaging spectrometer
1. INTRODUCTION
The airborne imaging spectrometer APEX (Airborne Prism
Experiment) is a dispersive pushbroom system designed to
contribute to the understanding of processes associated with
air, water and land at local and regional scale in support of
global applications and to support the preparation,
simulation, calibration and validation of future spaceborne
imaging spectrometers [1].
APEX has been designed to deliver imaging spectroscopy
data characterized by high spectral, radiometric and
geometric accuracy. The targeted data accuracy relies upon
three main factors: (a) provision of a highly precise
instrument by the industrial partners, (b) detailed instrument
calibration of the instrument characteristics by means of the
Calibration Home Base (CHB) at DLR, Oberpfaffenhofen,
Germany and (c) data calibration and higher level product
generation at the APEX Processing and Archiving Facility
(PAF) at VITO in Mol, Belgium [2].
The APEX system is currently undergoing an extensive
phase of assessing its system performance, following the
final acceptance of the principal investigators and ESA.
In this paper, we describe the main aspects of the APEX
PAF with a focus on product generation.
2. DATA ARCHIVING
Flight scenes in their raw format and calibration data are the
foundation of the data chain. Any higher-level product can
be reprocessed based on the raw input and its archiving is
thus compulsory.
The APEX archiving system is based on iSCSI SAN
(Storage Area Network) storage. All data are managed by
entries in a processing and products database, implemented
as a relational schema in a MySQL database [3].
3. CALIBRATION PROCESS
The calibration of a measuring instrument or system is the
fundamental tool to ensure the reliability of measurements,
in terms of accuracy and traceability. The instrument and
data calibration concept and process determine the
performance characteristics of the overall system [4].
The accuracy of the APEX data processing results relies on
two fundamental steps: (a) the instrument calibration
concept, its application by means of adequate measurement
procedures applied at the CHB, the consequent
determination of the calibration coefficients, and (b) the
integration of this information into the processing chain
(Fig. 1).
The traceability is provided by the calibration laboratory.
The CHB is a purpose built facility for calibration and
characterization of imaging spectrometers, whose equipment
and setup delivers inputs to the instrument with certified
high degree accuracy and repeatability, for the acquisition of
spectral, radiometric and geometric calibration data. The
CHB high quality standard combines with the
automatization possibility to minimize the duration the