4 Final Report - Emits - ESA

4 Final
Report
FoV (300/157 = 1.9), i.e. 20 m (nadir). Since no SNR requirements were derived from user needs, a
value of 150 was selected for all VNIR channels, consistently with PAN channel and Sentinel 2
requirements (around 150 and up to 170 for some channels).
The instrument parameters for each channel are summarised in Figure 4.3-2. The GSD at the
maximum latitude where full performance is required is recalled in column 3.The MTF at Nyquist
frequency in is given in column 4, showing that the 10% requirement is met for all multispectral
channels. For the PAN channel, despite relaxation to 5%, the requirement is met without much
margin. This clearly demonstrates that the maximum resolution achievable with a 1.5 m telescope is
reached for this channel (10.5 m nadir).
1 2 3 4 5 6 7 8 9
Mission Channel
GSD at 52°N
(m)
MTF at
Nyquist
Final
SNR
Nb
of images
Post
Integration
Integ. Time
of image (s)
Channel acq.
time (s)
Disaster VNIR2 40 0.117 150 1 No 0.009 0.088
Disaster VNIR3 40 0.116 150 1 No 0.011 0.088
Disaster VNIR4 40 0.115 150 1 No 0.014 0.088
Disaster VNIR5 40 0.111 150 1 No 0.017 0.088
Disaster VNIR6 40 0.110 150 1 No 0.021 0.088
Disaster VNIR7 21 0.051 300 4 No 0.013 0.352
Disaster VNIR10 40 0.111 150 1 No 0.029 0.088
Disaster VNIR11 40 0.115 150 1 No 0.005 0.088
Disaster VNIR12 40 0.112 150 1 No 0.034 0.088
Disaster VNIR13b 40 0.113 150 1 No 0.034 0.088
Disaster VNIR14 40 0.098 150 1 No 0.073 0.088
Disaster VNIR15 40 0.117 150 1 No 0.011 0.088
Disaster VNIR16 40 0.110 150 1 No 0.027 0.088
Figure 4.3-2: Performances for Disaster Monitoring
The SNR obtained after accumulation of the number of successive images indicated in column 6 is
given in column 5. All multi-spectral channels can be acquired in a single image, i.e. without postintegration,
while keeping good image quality (MTF at Nyquist > 10%, see column 4). The integration
time of individual raw images is given in column 8. The time to acquire the channel (last column) is
obtained by multiplying the number of images by the largest value between the integration time and
the array readout time.
4.3.2.2 Marine applications
For marine applications with challenging SNR requirements, 2x2 pixel binning is used to increase the
collected signal, so the final ground resolution is 40 m nadir and 80 m at 52.5°N, well within the goal
requirement of 100 m. Thanks to this lower resolution, the requirements on the pointing stability during
imaging periods can be relaxed to 10 µrad/s, allowing to largely reduce the tranquilisation time
following a slew manoeuvre. For channels with high SNR requiring long exposure time, the image
acquisition is split in several successive images to avoid pixel saturation & image smear due to
pointing drift. These images are summed on-board, with for the most critical ones (UV-blue channels)
compensation of the image motion (so-called "post-integration").
The instrument parameters for each channel are summarised in Figure 4.3-3. The MTF at Nyquist
requirement (10%) is met with good margins for all channels. Post-integration with LoS motion
compensation is only required for the bands of the UV-blue focal plane (UV1 to VNIR5). Other bands
require several images to avoid saturation at typical flux, these images are simply added in the on-
Doc. No: GOC-ASG-RP-002 Page 4-31
Issue: 2
Date: 13.05.2009 Astrium GmbH