|
Level-1 browse images are provided to enable overviewing pf observed images at reduced resolution, and have image values relative to radiance.
Users can obtain a rough impression of the cloud/snow coverage and objects on the ground surface by simply looking at the Level-1 browse images.
Level-1 browse products are normally used for retrieval of Level-1 products.
One type of color browse images will be generated for each of three subsystems (VNIR, SWIR, and TIR) in all Level-1 products.
Band 1, 2, 3N, Band 4, 5, 9 and Band 10, 12, 14 are assigned to the blue, green and red component in the browse images
for VNIR, SWIR and TIR subsystems, respectively, as shown in Table 5-5.
The resolution of one pixel in Level-1 images in all subsystems is reduced into about 309 m/pixel using average sampling.
The sampled image is put in a 224 pixel by 208 line frame.
This frame size of browse images corresponds to about 5.1 cm by 4.7 cm on the display monitor when a 17 inch monitor with
XGA mode(1024 x 768 dots) is used.
Geometric correction, including map projection, is not performed for browse image.
The browse images are always oriented northwards regardless of the spacecraft flight direction (descending or ascending) as shown in Figure 6-1.
Skew distortion caused by the Earth's rotation is also corrected. Figure 4-8 shows orientation of browse image and Level-1A images.
Figure 6-1 Orientation of browse images
Level-1A data values are radiometrically corrected in the same way as for Level-1B.
The radiance is then rescaled into an 8-bits range using linear density stretching.
Finally, the 8-bits color image is compressed using the JPEG lossy method. This shrinks the data volume in about 1/15
Table 6-1 Specifications of Level-1 Browse Images.
| Target Data |
| |
target products |
all Level 1A products |
| target subsystems |
one browse image per VNIR, SWIR and TIR respectively 3 bands per a subsystem |
| target bands |
default bands combination: VNIR=1,2,3N, SWIR=4,5,9, TIR=10,12,14 |
| Radiometric Correction |
the same radiometric correction as Level 1B processing |
| Contrast Conversion |
| |
conversion method |
linear contrast conversion |
| conversion coeff. |
decided based on percentile method and simple observation model (named as median method) |
Image Type of Browse
Color Assignment |
color image
Default assignment.
|
VNIR |
SWIR |
TIR |
| B |
1 |
4 |
10 |
| G |
2 |
5 |
12 |
| R |
3N |
9 |
14 |
|
| Geometric Correction |
| |
map projection |
no apply |
| skew correction |
done |
| bands registration |
Intra/inter-bands registration |
| others |
Stagger alignment and sampling delay are considered. |
| Image Size of Browse |
| |
frame size |
224 pixels * 208 lines
(5.1cm * 4.7cm on a display monitor: when 17" monitor and 1024dots/window) |
| effective size |
about 199 pixels * 204 lines for VNIR and SWIR
about 204 pixels * 204 lines for TIR
(4.5-4.6cm * 4.6cm on user's display monitors
:when 17"monitor and 1024 dots/window) |
| Sampling |
| |
sampling rate |
about 1/20.59(VNIR), 1/10.29(SWIR), 1/3.43(TIR) |
| sampling interval |
about 309m on the ground |
| sampling method |
average sampling |
| Data Compression |
| |
compression method |
JPEG |
| Q-value |
50 |
| compression ratio |
about 1/15 (estimation) |
|
