ON-ORBIT SPATIAL RESOLUTION ESTIMATION OF CBERS-1 CCD IMAGING
SYSTEM FROM BRIDGE IMAGES
K. Bensebaa, G. J. F. Banon, L. M. G. Fonseca
Image Processing Division - National Institute for Space Research (INPE)
Av. dos Astronautas, 1758, 12201-027 Sào José dos Campos, Brazil
(camel, banon, Leila) (dpi.inpe.br
Commission WG I/2
KEY WORDS: CCD Camera, Spatial Resolution, Estimation, Modelling, Simulation, Measurements, Targets.
ABSTRACT:
The first China-Brazil Earth Resources Satellite (CBERS) was launched in 1999 and recently was substituted by CBERS-2. CBERS-
| and CBERS-2 have the same specifications and carry three sensors which combine features that are specially designed to cover the
broad range of space and time scales involved in the monitoring and preservation of the ecosystem: Wide Field Imager (WFI), High
Resolution CCD Camera (CCD) and Infrared Multispectral Scanner (IRMSS). In general, the imaging systems cause a blurring due
to the cumulative effects of the instrumental optics (diffraction, aberrations, focusing error) and image motion induced by the
movement of the satellite during imaging. This blurring can be understood by describing the imaging system in terms of the Point
Spread Function (PSF). For a satellite sensor, the knowledge of the point spread function is of fundamental importance since it
enables an objective assessment of spatial resolution through the parameter known as EIFOV (Effective Instantaneous Field of
View). This paper describes an original approach to estimate the spatial resolution of the CBERS-1 CCD camera. The imaging
system point spread function is modeled as a separable gaussian function. The PSF is estimated using images of Rio-Niteroi Bridge
in Rio de Janeiro (Brazil) and the Lake Pontchartrain Causeway in Louisiana (United States). The results showed that the spatial
resolution in across-track direction is outside the specifications for all bands while the spatial resolution in along-track direction is
within the specification for all bands, except the band 4.
1. INTRODUCTION
The CBERS (China-Brazil Earth Resources Satellite)
cooperative program has been jointly developed by China and
Brazil for the building up a set of remote sensing satellites.
CBERS-1 and CBERS-2 satellites were launched on October
14, 1999 and October 21, 2003, respectively. CBERS-1 carries
onboard sensors, which combine features that are specially
designed to cover the broad range of space and time scales
involved in the monitoring and preservation of the ecosystem.
During image acquisition, the imaging systems cause a blurring
due to the cumulative effects of the instrumental optics
(diffraction, aberrations, focusing error) and image motion
induced by the movement of the satellite (Leger et al. 2002).
This blurring effect can be modelled by the Point Spread
Function (PSF) or by the Modulation Transfer Function (MTF)
in the frequency domain.
The PSF and the MTF are of great importance in determining
the spatial resolution of a system that is usually defined as its
half-power response width (Bretschneider 2002). In general, the
spatial response is estimated from the PSF in terms of the
parameter known as EIFOV (Effective Instantaneous Field of
View) (Slater, 1980). When the PSF is approximated by a
gaussian function with standard deviation o, the EIFOV is
calculated as 2.666 (Banon and Santos, 1993). Storey (2001)
has provided a methodology to measure the Landsat-TM on-
orbit spatial response using ground target such as bridges. Choi
and Helder (2001) have used as targets airport runway and a
tarp placed on the ground for on-orbit MTF measurement of
IKONOS satellite sensor.
Before launching, band 4 (0,77 - 0,89 um) of the CBERS-1
CCD camera presented a myopia distortion due to a problem in
the camera assembly. At this time, some image simulation tests
were performed in order to check the possibility to improve its
resolution spatial through restoration technique (Banon and
Fonseca, 1998).
This paper describes an approach for the CBERS-1 CCD
camera in-flight spatial resolution assessment. The CCD spatial
response is modeled as a separable gaussian function in along-
track and across-track directions of the satellite. On-orbit
images of the Rio-Niteroi Bridge in Rio de Janeiro (Brazil) and
the Lake Pontchartrain Causeway in Louisiana (United States)
were used to estimate the spatial resolution in the along-track
and across-track directions, respectively.
2. CBERS-1 OVERVIEW
CBERS-1 satellite carries on-board a multisensor payload with
different spatial resolutions called: WFI (Wide Field Imager),
IRMSS (Infrared MSS) and CCD (Charge Coupled Device)
camera. The high-resolution CCD Camera has 4 spectral bands
from visible light to near infrared and one panchromatic band
(Table. 1). It acquires the earth ground scenes by pushbroom
scanning, on 778 km sun-synchronous orbit and provides
images of 113 km wide strips with sampling rate of 20 meters at
nadir.
Spectral Bands | Number | Wavelength
Blue BI 0,45 - 0,52
Green B2 0,52 - 0,59
Red B3 0,63 - 0,69
Near-Infrared B4 0,77 - 0,89
Pan. B5 0,51 - 0,73
Table 1. Spectral bands of the CCD sensor.
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