6 research outputs found
Spatio-temporal variability of sugarcane fields and recommendations for yield forecast using NDVI
PLEIADES-HR SYSTEM PRODUCTS PERFORMANCE AFTER IN-ORBIT COMMISSIONING PHASE
Launched on 2011, December 16th by the second Soyuz operated in French Guiana, PLEIADES-HR acquired its first high
resolution images 3 days after. The PLEIADES program is a space Earth Observation system led by the French Space Agency
(CNES), it provides the first european high resolution satellite which will simultaneously acquire in Panchromatic and Multi-
Spectral modes 20 km wide images with a 70 cm nadir resolution.
Imaging capabilities have been highly optimized in order to acquire, in the same pass, along-track mosaics, stereo pairs and triplets,
and multi-targets. Ground segment processes automatically data to ensure operational requirements and quick access to images for
the users. Since ground processing capabilities have been taken into account very early in the mission development, it has been
possible to relax some costly on-board components requirements, in order to achieve a cost effective on-board/ground compromise.
Starting from the PLEIADES system and on board characteristics, this paper first presents an overview of ground segment functional
breakdown. Then it focuses more precisely on the different levels of products and associated processing performances. Finally the
paper shows how appropriate ground processing systems allowed CNES Image Quality team to assess radiometric and geometric
performances during the 6 first months of PLEIADES 1A
AUTOMATIC AND GENERIC MOSAICING OF MULTISENSOR IMAGES: AN APPLICATION TO PLEIADES HR
In the early phase of the Pleiades program, the CNES (the French Space Agency) specified and developed a fully automatic
mosaicing processing unit, in order to generate satellite image mosaics under operational conditions. This tool can automatically put
each input image in a common geometry, homogenize the radiometry, and generate orthomosaics using stitching lines.
As the image quality commissioning phase of Pleiades1A is on-going, this mosaicing process is being tested for the first time under
operational conditions. The French newly launched high resolution satellite can acquire adjacent images for French Civil and
Defense User Ground Segments. This paper presents the very firsts results of mosaicing Pleiades1A images.
Beyond Pleiades’ use, our mosaicing tool can process a significant variety of images, including other satellites and airborne
acquisitions, using automatically-taken or external ground control points, offering time-based image superposition, and more. This
paper also presents the design of the mosaicing tool and describes the processing workflow and the additional capabilities and
applications
SENTINEL-2 LEVEL 1 PRODUCTS AND IMAGE PROCESSING PERFORMANCES
In partnership with the European Commission and in the frame of the Global Monitoring for Environment and Security (GMES)
program, the European Space Agency (ESA) is developing the Sentinel-2 optical imaging mission devoted to the operational
monitoring of land and coastal areas.
The Sentinel-2 mission is based on a satellites constellation deployed in polar sun-synchronous orbit. While ensuring data continuity
of former SPOT and LANDSAT multi-spectral missions, Sentinel-2 will also offer wide improvements such as a unique combination
of global coverage with a wide field of view (290 km), a high revisit (5 days with two satellites), a high resolution (10 m, 20 m and
60 m) and multi-spectral imagery (13 spectral bands in visible and shortwave infra-red domains).
In this context, the Centre National d'Etudes Spatiales (CNES) supports ESA to define the system image products and to prototype
the relevant image processing techniques.
This paper offers, first, an overview of the Sentinel-2 system and then, introduces the image products delivered by the ground
processing: the Level-0 and Level-1A are system products which correspond to respectively raw compressed and uncompressed data
(limited to internal calibration purposes), the Level-1B is the first public product: it comprises radiometric corrections (dark signal,
pixels response non uniformity, crosstalk, defective pixels, restoration, and binning for 60 m bands); and an enhanced physical
geometric model appended to the product but not applied, the Level-1C provides ortho-rectified top of atmosphere reflectance with a
sub-pixel multi-spectral and multi-date registration; a cloud and land/water mask is associated to the product. Note that the cloud
mask also provides an indication about cirrus. The ground sampling distance of Level-1C product will be 10 m, 20 m or 60 m
according to the band. The final Level-1C product is tiled following a pre-defined grid of 100x100 km2, based on UTM/WGS84
reference frame.
The stringent image quality requirements are also described, in particular the geo-location accuracy for both absolute (better than
12.5 m) and multi-temporal (better than 0.3 pixels) cases.
Then, the prototyped image processing techniques (both radiometric and geometric) will be addressed.
The radiometric corrections will be first introduced. They consist mainly in dark signal and detector relative sensitivity correction,
crosstalk correction and MTF restoration. Then, a special focus will be done on the geometric corrections. In particular the
innovative method of automatic enhancement of the geometric physical model will be detailed. This method takes advantage of a
Global Reference Image database, perfectly geo-referenced, to correct the physical geometric model of each image taken. The
processing is based on an automatic image matching process which provides accurate ground control points between a given band of
the image to refine and a reference image, allowing to dynamically calibrate the viewing model. The generation of the Global
Reference Image database made of Sentinel-2 pre-calibrated mono-spectral images will be also addressed.
In order to perform independent validation of the prototyping activity, an image simulator dedicated to Sentinel-2 has been set up.
Thanks to this, a set of images have been simulated from various source images and combining different acquisition conditions and
landscapes (mountains, deserts, cities …).
Given disturbances have been also simulated so as to estimate the end to end performance of the processing chain.
Finally, the radiometric and geometric performances obtained by the prototype will be presented.
In particular, the geo-location performance of the level-1C products which widely fulfils the image quality requirements will be
provided