The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
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better than 100 m by ground processing. The sensors’ 1024 
pixel in spatial direction result in a swath width of 30 km. 
The EnMAP ground segment comprises: 
• The mission operations system controlling the satellite and 
instrument. 
• The payload ground system responsible for data reception, 
handling, archiving, and delivery as well as for the user 
interfaces for observation and product orders. 
• The calibration, processor chain, and validation system 
capable of calibrating the sensor, generating calibrated 
hyperspectral data products at several processing levels, 
and validating these products. 
In this paper we focus on the calibration, processing chain, and 
validation for the EnMAP mission. 
1.2 Overview of the Calibration, Validation, and 
Processing Chain 
Figure 1. illustrates how the calibration and validation activities 
as well as the processing chain interact in order to generate 
high-quality and consistent products. 
Other Mission Image Data 
Figure 1. Calibration, Validation, and Processing Chain 
The EnMAP level 0 processor (see section 3.1) creates the 
EnMAP level 0 products, which are then stored for long term 
archiving along with the orbit, and attitude products that are 
provided by the mission operations system. The calibration 
facility is in charge of creating and maintaining - if necessary - 
the calibration products (spectral, radiometric, and geometric). 
Therefore, it receives parts of the level 0 products, such as dark 
value, internal lamps, and sun measurements. (Due to the strong 
relation with its validation, the geometric calibration is 
described in section 4.2 while spectral and radiometric 
calibration is described in section 2.) 
For the EnMAP level 1 to EnMAP level 2 product generation, 
the corresponding EnMAP level 0, calibration, orbit, and 
attitude products are retrieved to start the processing chain (see 
section 3). Image products will be sent periodically to the 
validation facility, which along with image data from other 
missions will carry out validation activities (see section 4.2). 
The results of these activities will be reported to the calibration 
facility to inform of the possible needs to update the calibration 
products. 
2. CALIBRATION 
During the complete mission lifetime the spectral and 
radiometric behavior of the sensor vary within narrow limits 
(e.g., Schwarzer, H. et al., 1998; Schwarzer, H. et al., 2003). 
However, the on-board calibration system allows processing of 
the data on ground to a spectral accuracy of better than 0.5 nm 
and radiometric accuracy of better than 5%. For this a full 
aperture diffuser mounted in front of the telescope is foreseen. 
Further calibration equipment, i.e. internal light sources, for 
frequent relative radiometric as well as spectral calibration 
measurements are installed in integrating spheres and coupled 
into the system via a calibration shutter mechanism located in 
front of the in-field separation unit. This mechanism also allows 
dark measurements before and after a data take sequence. Dark 
space calibrations will verify these dark measurements. 
Complemented by pre-launch calibration and characterization 
these analyses will deliver a detailed and quantitative 
assessment of possible changes of spectral and radiometric 
characteristics of the hyperspectral instrument, e.g. due to 
degradation of single elements. (See section 4.2 for geometric 
calibration and validation.) Hence EnMAP can always achieve 
comparable measurements with respect to data from the same 
and from other calibrated missions. 
One of the tasks for calibration after launch is therefore to 
adjust the pre-launch and to establish the post-launch 
calibration reference for all essential measurement modes, i.e. 
• Dark Value Measurements, 
• Internal Lamps Measurements, and 
• Sun Measurements. 
The housekeeping data help to check the status and health of 
the HSI during calibration measurements and to correct for 
systematic effects, e.g. temperatures. 
2.1 Dark Value Measurements 
The measurement of dark values for all spatial and spectral 
pixels is the most frequent measurement to characterize the HSI. 
These values are needed both for control of the calibration as 
well as for the EnMAP level 1 processing of the data (see 
section 3). 
The following dark value measurements will be performed 
during the whole mission lifetime 
• at the beginning and end of each datatake of the Earth, 
• at the beginning and end of each datatake of the internal 
lamps, and 
• at the beginning and end of each datatake of the Sun. 
These dark values are averaged from the single read-outs for 
each spatial and spectral pixel and then checked to be in a given 
range around the dark value reference. The averaged values are 
then used for dark value correction in further processing as well 
as for analysis of the internal lamp and Sun measurements. If 
outliers are found, they must be analyzed for possible causes, 
e.g. damaged pixel, spikes, and changes in the detectors’ 
sensitivity. 
2.2 Internal Lamps Measurements 
The measurements of the several light sources inside the 
instrument will be operated at different currents and will 
illuminate the entire focal plane, but only a part of the optical 
path (starting with the entrance slit of the spectrometer) is used. 
The measurements allow checking for spectral and radiometric 
stability of the instrument or relative changes in the behavior of 
the focal plane. A measurement consists of dark value 
measurements and several illumination levels by the selected 
light sources. Each lamp has a certain bum-in time after voltage 
changes until it reaches the final light level. From all read-outs 
of one illumination level therefore a certain number of read-outs 
at the beginning have to be skipped. All other read-outs are