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COMPRESSION SPECIFICATION FOR EFFICIENT USE OF HIGH RESOLUTION 
SATELLITE DATA 
Emmanuel Christophe, Carole Thiebaut and Christophe Latry 
CNES DCT/SI/AP Bpi 1219 
18 av E. Belin, 31401 Toulouse Cedex 09 
{emmanuel.Christophe, carole.thiebaut, Christophe.latry}@cnes.fr 
Commission IV/9 
KEY WORDS: Compression, high resolution,optical, JPEG 2000, data transfer 
ABSTRACT: 
For an efficient usage and distribution of high resolution satellite images, several problems need to be solved. The issue comes with 
the increasing size of these data. Constraints are different than those of the on-board compression, thus different solutions can be 
selected. For on-board compression, the main constraints are the computational complexity and the rate attainable with qualified space 
equipments. For on-the-ground compression, computational constraints are not so strong, but particular care is needed to make sure 
that the chosen format is widely spread and that users will be able to exploit these data easily. 
1 INTRODUCTION 
3 END-USERS REQUIREMENTS 
For an efficient usage and distribution of high resolution satel 
lite images, several problems need to be solved. The issue comes 
with the increasing size of these data. A standard scene from 
the Pleiades satellite, the coming optical high resolution satel 
lite from CNES, will typically represent 14 GB of data (more 
4 x 4 pixels in 4 spectral bands on 16 bits). The difficul 
ties with such data do not occur only in the distribution process, 
but also in the processing steps, data selections, quality assess 
ment. 
End-users need the access to derived products from the satellite 
image. For a question of cost or efficiency, the high resolution 
is often not required on the full scene. One of the most valuable 
product is the high resolution on a specific area (city, disaster 
area,...) and a lower resolution around to give a precise idea of the 
context of the scene. Ideally, this higher resolution information 
should be available on-demand according to the user’s decision 
on the lower resolution level. 
Constraints are different than those of the on-board compression, 
thus different solutions can be selected. For on-board compres 
sion, the main constraints are the computational complexity and 
the rate attainable with qualified space equipments. For on-the- 
ground compression, computational constraints are not so strong, 
but particular care is needed to make sure that the chosen format 
is widely spread and that users will be able to exploit these data 
easily. 
Fast and multiresolution data access is also necessary. When vi 
sualized at full resolution, one scene represents more that 700 
computer screens. In these conditions, finding the valuable infor 
mation is like looking for a needle in a haystack. 
This multiresolution feature is also very valuable for the steps of 
data quality assessment. For example, the full resolution is not 
necessary when establishing the cloud coverage notation. 
2 SATELLITE DATA SPECIFICITIES 
Most of popular compression formats cannot be used for satellite 
data which often reach their limits. The first problem is the size 
of the data: already often reaching 30000 pixels per dimension, 
it is easy to foresee products exceeding 2 1 pixels. The second 
problem is the dynamic range of the values: instead of the more 
common 8 bits, these data are often coded on 12 bits to be able 
to cover the wide dynamic range of observed scenes. Finally, 
these data often comprise at least four spectral bands while most 
compression formats target the typical color images with three 
components (Fig. 1). 
Another strong requirement is the possibility to include complex 
metadata directly on the compressed streams. Apart from the 
essential localization information, additional data corresponding 
to some data extraction results (classification, road extraction, 
clouds mask...) or coming from vectorized map should be avail 
able in the images. 
In some situations, fast access to the data is critical. For example, 
when the image is to be used in the context of a crisis (hurricane, 
tsunami, flooding, earthquake) to help to organize the rescue, it is 
inconceivable to waste precious hours in inefficient data transfer. 
The JPEG 2000 standard was designed to answer these limita 
tions (Taubman and Marcellin, 2002). The facts that this is a well 
accepted standard and that it is starting to be widely available 
through numerous and well performing implementations make 
it a good candidate for satellite data distribution. However, this 
standard comprises many options and not all are adapted for high 
resolution satellite images. Thus, it is necessary to explore these 
possibilities to find the right combination ensuring an efficient 
access for the end-user with a limited complexity. 
New data distribution schemes can also arise from advanced data 
structures. For example, the full product could be delivered on a 
DVD with part of it encrypted. Unlocking the full product would 
consist in buying the key from the data provider which results in 
a near instantaneous transaction. The main advantage is that the 
low resolution data can be delivered for a very reasonable price 
and the full resolution with a very short delay according to the 
image processing requirements. 
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