All of the USGS browse images are subsampled JPEGs of selected bands from the
actual sensor data. The band combination, stretch, and resolution of the browse
will vary according to each sensor:
Within the Browse Image Viewer, the browse images are displayed in Lambert
Azimuthal Equal Area Projection unless otherwise noted.
ASTER Level-1B VNIR and TIR
The ASTER L1B VNIR (Level-1B Visible Near Infra-Red) browse images
are displayed as a 3N, 2,1 (RGB) color composite.
The ASTER L1B TIR (Level-1B Thermal Infra-Red) browse images are
displayed as a 13,12,10 (RGB) color composite. The TIR browses
displayed on GloVis are from selected night-acquired images.
VNIR and TIR bands may be available for day and night-acquisition
images; however, you need to review the metadata for each scene you
select to determine what bands are available for that scene.
The orderable data is ASTER L1B Registered Radiance at the
Sensor (
http://lpdaac.usgs.gov/aster/ast_l1b.html). This product
contains radiometrically calibrated and geometrically co-registered
data for all the channels acquired previously through the
telemetry streams of the 3 different telescopes in Level-1A
(
http://lpdaac.usgs.gov/aster/ast_l1a.html).
The VNIR pixels are subsampled to a resolution of approximately 90
meters from the original 15-meter data. TIR browse images are not
subsampled.
For the full-resolution (90 meter) browses, the images are JPEG
compressed with an average file size of ~85K. The 400 meter
display mode browse images are GIFs with an average file size
of ~25K. The 1000 meter display mode, browse images are
GIFs with an average file size of ~5K.
The original browse images (viewed in a separate browser window)
are in the UTM projection rotated to the satellite orientation.
EO-1 ALI
The Advanced Land Imager (ALI) browse images are generated from the
Level 1 radiometrically corrected data and displayed as a 4,3,1
(RGB) band combination.
Pixels are subsampled to a resolution of 240 meters from the
original 30-meter data (a factor of 8 in each direction).
The exact scene length will vary. The two most typical scene
lengths will be approximately 42 km for a standard scene and
approximately 185 km for an extended scene.
Each band is linearly stretched between the 1% and 97% histogram
values.
For the full-resolution browses, the images are JPEG compressed
with an average file size of 25K. For the 1000 meter display mode,
the browse images are GIFs with an average file size of 6K.
The original browse images (viewed in a separate browser window)
are Level 1 radiometrically corrected browse in satellite
orientation.
EO-1 Hyperion
The Hyperion browse images are generated from the Level 0 (raw)
data and displayed as a RGB (40:31:13) band combination. Note that
some browse are single band browse created from band 40. These
browse will eventually be replaced with RGB browse.
Pixels are subsampled to a resolution of 120 meters from the
original 30-meter data (a factor of 4 in each direction).
The exact scene length will vary. The two most typical scene
lengths will be approximately 42 km for a standard scene and
approximately 185 km for an extended scene.
The Hyperion browses have had the dark calibration subtracted and
the gains have been applied. Each band is linearly stretched
between the 1% and 97% histogram values. The data is then scaled
from 12 bits to 8 bits.
For the full-resolution browse, the images are JPEG compressed
with an average file size of 25K. For the 1000 meter display mode,
the browse images are GIFS with an average file size of 2K.
The original browse images (viewed in a separate browser window)
are Level 1 radiometrically corrected browse in satellite
orientation.
Landsat 7 ETM+
Image acquired from June 1999 - May 2003 displayed as a 5,4,3 (RGB)
composite.
Pixels are subsampled to a resolution of 240 meters from the
original 30-meter data.
Each Landsat 7 scene is color-stretched based on individual scene
content. This may result in an apparent mismatch of colors between
scenes.
For the full-resolution browses, the images are JPEG compressed
with an average file size of ~130K. For the 1000 meter display
mode, the browse images are GIFs with an average file size of ~35K.
The original browse images (viewed in a separate browser window)
are raw browse in satellite orientation.
Landsat 7 ETM+ Scan Line
Corrector (SLC) Off
Images acquired after Landsat 7 suffered the SLC failure (July 2003
- present) display as a 5,4,3 (RGB) composite.
The effects of the SLC failure is difficult to see in the
browse images. The scene edge will contain alternating scan lines
of missing data or duplicated data. The precise location of the
affected scan lines will vary from scene to scene. An effort is
currently underway to create enhanced browse images that show the
missing data. As the new browse are created, they will be shown in
GloVis.
The "Show Browse" option includes annotation that illustrates the
approximate impact of the SLC-off image effects.
The SLC-off data set is similar to the Landsat 7 ETM+ data set.
The image are displayed as a 5,4,3 (RGB) composite with 2% linear
stretch.
Pixels are subsampled to a resolution of 240 meters from the
original 28.5-meter data.
All Landsat 4 and 5 images use a standardized 2% linear stretch.
In the full resolution browse view, the Landsat 4 and 5 browse
images will appear to be 1/4 the size of the Landsat 7 browse
images, but the actual TM scene will cover approximately the same
area (183 x 170 km).
For the full-resolution browses, the images are JPEG compressed
with an average file size of ~50K. For the 1000 meter display mode,
the browse images are GIFs with an average file size of ~35K.
The original browse images (viewed in a separate browser window)
are raw browse in satellite orientation.
Landsat 1-5 MSS
The images are displayed as a 4,2,1 (RGB) composite with 2% linear
stretch for Landsat 4 - 5 MSS; 7,5,4 (RGB) for Landsat 1-3 MSS.
Pixels are subsampled to a resolution of 240 meters from the
original nominal 80-meter data.
In the full resolution browse view, the MSS browse images will
appear to be 1/4 the size of Landsat 7 browse images, but the actual
MSS scene will cover approximately the same area (185 x 170 km).
For the full-resolution browses, the images are JPEG compressed
with an average file size of ~50K. For the 1000 meter display mode,
the browse images are GIFs with an average file size of ~35K.
Landsat Orthorectified ETM+
The images are Landsat 7 ETM+ and do not show the final
Orthorectified product. They are displayed as a 5,4,3 (RGB)
color composite.
Pixels are subsampled to a resolution of 240 meters from the
original 30-meter data.
Each Landsat 7 scene is color-stretched based on individual
scene content. This may result in an apparent mismatch of colors
between scenes.
For the full-resolution browses, the images are JPEG compressed
with an average file size of 147K. For the 1000 meter display mode,
the browse images are GIFs with an average file size of 8k.
The original browse images (viewed in a separate browser window)
are raw browse in satellite orientation.
Landsat Orthorectified Pansharpened
ETM+
The images are Landsat 7 ETM+ and do not show the final
Orthorectified product. They are displayed as a 7,4,2 (RGB)
color composite.
Pixels are subsampled to a resolution of 240 meters from the
original 30-meter data.
Each Landsat 7 scene is color-stretched based on individual
scene content. This may result in an apparent mismatch of colors
between scenes.
For the full-resolution browses, the images are JPEG compressed
with an average file size of 147K. For the 1000 meter display mode,
the browse images are GIFs with an average file size of 8k.
The original browse images (viewed in a separate browser window)
are raw browse in satellite orientation.
Landsat Orthorectified TM
The Orthorectified TM browse images are displayed as a 7,4,2 (RGB)
color composite.
Pixels are subsampled to a resolution of 480 meters from the
original 30-meter data.
For the full-resolution browses, the images are JPEG compressed
with an average file size of 38K. For the 1000 meter display mode,
the browse images are GIFs with an average file size of 23K.
The original browse images (viewed in a separate browser window)
were generated from full-resolution data that is orthorectified
and UTM-projected, using the World Geodetic System 1984 datum.
MODIS
The images are displayed as a 1,4,3 (RGB).
The images generally cover a 10° x 10°.
Pixels are subsampled to a resolution of approximately 10
kilometers from the original 5 kilometer data.
Each scene is color-stretched based on individual scene content.
This may result in an apparent mismatch of colors between scenes.
The 10 kilometer display browse images are jpgs with an average
file size of 5K. The full-resolution browse images are JPEG
compressed with an average file size of 30K.
The full-resolution browse images, which can be viewed in a
separate browser-window, are the same as the 5-kilometer images
shown in the applet. The only exception are datasets that have
an annotation on the bottom of the browse. These browse images
will cover more area than what is shown in the applet.
The browse are displayed in the sinusoidal projection.
The short MODIS Aqua dataset names used in
the GloVis site stand for the following longer dataset names:
MYD09A1
MODIS/Aqua Surface Reflectance 8-Day L3 Global 500m SIN
Grid
MYD11A1 Day
MODIS/Aqua Surface Temperature/Emissivity Daily L3
Global 1km SIN Grid Day
MYD11A1 Night
MODIS/Aqua Surface Temperature/Emissivity Daily L3
Global 1km SIN Grid Night
MYD11B1 Day
MODIS/Aqua Surface Temperature/Emissivity Daily L3
Global 5km SIN Grid Day
MYD11B1 Night
MODIS/Aqua Surface Temperature/Emissivity Daily L3
Global 5km SIN Grid Night
MYD13A1 EVI
MODIS/Aqua Vegetation Indices 16-Day L3 Global 500m SIN
Grid EVI
MYD13A1 NDVI
MODIS/Aqua Vegetation Indices 16-Day L3 Global 500m SIN
Grid NDVI
MYD13A2 EVI
MODIS/Aqua Vegetation Indices 16-Day L3 Global 1km SIN
Grid EVI
MYD13A2 NDVI
MODIS/Aqua Vegetation Indices 16-Day L3 Global 1km SIN
Grid NDVI
MYD14A1
MODIS/Aqua Thermal Anomalies/Fire Daily L3 Global 1km
SIN Grid
MYD14A2
MODIS/Aqua Thermal Anomalies/Fire 8-Day L3 Global 1km
SIN Grid
MYD15A2 FPAR
MODIS/Aqua Leaf Area Index/FPAR 8-Day L4 Global 1km SIN
Grid FPAR
MYD15A2 LAI
MODIS/Aqua Leaf Area Index/LAI 8-Day L4 Global 1km SIN
Grid LAI
MCD43B1
MODIS/Terra+Aqua BRDF/Albedo Model-1 16-Day L3 Global
1km SIN Grid
MCD43B3
MODIS/Terra+Aqua Albedo 16-Day L3 Global 1km SIN
Grid
MCD43B4
MODIS/Terra+Aqua Nadir BRDF-Adjusted Reflectance 16-Day
L3 Global 1km SIN Grid
The short MODIS Terra dataset names used in
the GloVis site stand for the following longer dataset names:
MOD09A1
MODIS/Terra Surface Reflectance 8-Day L3 Global 500m
SIN Grid
MOD11A1 Day
MODIS/Terra Surface Temperature/Emissivity Daily L3
Global 1km SIN Grid Day
MOD11A1 Night
MODIS/Terra Surface Temperature/Emissivity Daily L3
Global 1km SIN Grid Night
MOD11B1 Day
MODIS/Terra Surface Temperature/Emissivity Daily L3
Global 5km SIN Grid Day
MOD11B1 Night
MODIS/Terra Surface Temperature/Emissivity Daily L3
Global 5km SIN Grid Night
MOD13A1 EVI
MODIS/Terra Vegetation Indices 16-Day L3 Global 500m SIN
Grid EVI
MOD13A1 NDVI
MODIS/Terra Vegetation Indices 16-Day L3 Global 500m SIN
Grid NDVI
MOD13A2 EVI
MODIS/Terra Vegetation Indices 16-Day L3 Global 1km SIN
Grid EVI
MOD13A2 NDVI
MODIS/Terra Vegetation Indices 16-Day L3 Global 1km SIN
Grid NDVI
MOD14A1
MODIS/Terra Thermal Anomalies/Fire Daily L3 Global 1km
SIN Grid
MOD14A2
MODIS/Terra Thermal Anomalies/Fire 8-Day L3 Global 1km
SIN Grid
MOD15A2 FPAR
MODIS/Terra Leaf Area Index/FPAR 8-Day L4 Global 1km SIN
Grid FPAR
MOD15A2 LAI
MODIS/Terra Leaf Area Index/LAI 8-Day L4 Global 1km SIN
Grid LAI
MOD43B1
MODIS/Terra BRDF/Albedo Model-1 16-Day L3 Global 1km SIN
Grid
MOD43B3
MODIS/Terra Albedo 16-Day L3 Global 1km SIN Grid
MOD43B4
MODIS/Terra Nadir BRDF-Adjusted Reflectance 16-Day L3
Global 1km SIN Grid
MCD43B1
MODIS/Terra+Aqua BRDF/Albedo Model-1 16-Day L3 Global
1km SIN Grid
MCD43B3
MODIS/Terra+Aqua Albedo 16-Day L3 Global 1km SIN
Grid
MCD43B4
MODIS/Terra+Aqua Nadir BRDF-Adjusted Reflectance 16-Day
L3 Global 1km SIN Grid
MRLC 2001 Terrain Corrected (TC) and
2001 Reflectance Adjusted (RA)
The images are Landsat 7 ETM+ and Landsat 4-5 TM images and do not
show the final MRLC product. They display as a 5,4,3 (RGB)
composite.
Pixels are subsampled to a resolution of 240 meters from the
original 30 meter data.
Each landsat 7 scene is color-stretched based on individual scene
content. This may result in an apparent mismatch of colors between
scenes.
For the full-resolution browses, the image are JPEG compressed with
an average file size of ~130K. For the 1000 meter display mode, the
browse images are GIFs with an average file size of ~35K.
The original browse images (viewed in a separate browser window) are
raw browse in satellite orientation.
MRLC 1992
The images are Landsat 4-5 TM images and do not show the final MRLC
product. They are displayed as a 5,4,3(RGB) composite with 2% linear
stretch.
Pixels are subsampled to a resolution of 240 meters from the
original 28.5 meter data.
In the full resolution browse view, the Landsat 4 and 5 browse
images will appear to be 1/4 the size of the Landsat 7 browse
images, but the actual TM scene will cover approximately the same
(183 x 170km).
For the full-resolution browses, the images are JPEG compressed
with an average file size of ~50K. For the 1000 meter display mode,
the browse images are GIFs with an average file size of ~35K.
The original browse images (viewed in a separate browser window) are
raw browse in satellite orientation.
NOTE: Because the browse images are processed from raw uncorrected data, the
positional accuracy of the scenes can only be expected to be accurate within a
few pixels at full resolution. These browse images are not intended for
analytical use, but only as a visual scene selection aid.
Q: Why is there so much color variation among the
Landsat 7 browse images?
A: A custom color stretch is performed on the raw Landsat 7 data,
based on individual scene content for bands 5, 4, and 3. Scenes from within
the same area and/or acquisition date may vary in band content (due to
differences such as cloud content or ground moisture), and this differing
content will cause variation in the results of the color stretch.
Q: Why do the Landsat 7 (ETM+) browse images look
so different from the Landsat 4-5 (TM) images?
A: Even though the band combination is the same, differences in the
browse processing will make the final images look very different between
the two sensors. Landsat 4-5 (TM) scenes have been subsampled to a much
lower resolution (480 meteres), with a standardized stretch applied.
Landsat 7 images are resampled to 240 meters, and each image has a
customized stretch applied based on individual scene content. The Landsat
4-5 TM images will also be approximately 1/4 the size, but the actual data
will cover approximately the same area as a Landsat 7 ETM+ image.
In spite of these differences between the browse images, data from the
two sensor types should be fairly comparable in data content, resolution,
and scene size.
Q: Why do some Landsat 7 (ETM+) browse images appear to
be split midway through a scene?
A: A linear shift in color is due to gain change in the sensor,
which occurs when the sensor encounters an area of consistently different
reflectance (for example, when the sensor encounters snowy regions or
highly reflective desert areas).
These artifacts will be apparent in the Landsat 7 browse, because the
browse image has been generated directly from raw uncalibrated data.
However, when the Landsat 7 order is placed, a calibration parameter file
containing all gain change information will be used to process the data.
Therefore, the appropriate gain and bias values will be incorporated into
the scene processing. These artifacts will not exist in the final
processed (Level 1) product.
Q: How is the cloud cover calculated, and why are
some scenes cloudy when the cloud cover is reported to be 0%?
A: The cloud cover index is an automated calculation which may
provide a useful estimate, but the algorithm is not always accurate when it
encounters snow, ice, water, or other unusual scene content. Haze, thin
clouds, and small clouds ("popcorn") can frequently be missed in the cloud
cover assessment.
Q: Where are the Landsat night scenes?
A: Landsat night acquisitions are not currently included in the
USGS Global Visualization tool. If you would like to search and order
Landsat night-time (ascending pass) scenes, they are available through Earth Explorer.
Q: Why are some Landsat TM scenes "missing" from the
browse viewer?
A: The USGS Global Visualization tool will only display scenes that
have browse images available in the inventory. Some scenes do exist in the
USGS archive, but they do not yet have a corresponding browse images that
has been processed. To access Landsat 5 TM data for which there is no
browse, you will need to run a search on Earth Explorer to
find the scene ID, and then contact Customer
Services. As TM browse images become available in the future, they
will be automatically added to the USGS Global Visualization tool.
Q: Why are there so few Landsat TM international
scenes?
A: The USGS Global Visualization tool will only display scenes
from the USGS archive. For many locations outside the U.S., there may be
scenes that were collected by the sensor but the data is not archived or
distributed by the USGS EROS Data Center. These scenes may still be
available from other International Ground
Stations. Please note that this data is not a product of the USGS EROS
Data Center, and therefore the prices, available formats, and/or processing
options may vary according to the data provider.
Q: Why are some of the Landsat TM browse images so
blocky?
A: Apparently, the color stretch used by the processing system to
create browse images for Landsat TM images does not perform well in areas
of low contrast. The resulting browse images are of very low quality and
probably do not indicate the real quality of the full resolution image.
Imagery containing snow, ice, and clouds may experience this problem.
There is nothing the USGS Global Visualization tool can do to correct this
problem since the original browse images show the problem.
Q: Why do some Landsat TM browse images appear pink/red?
A: Landsat TM browse images are created using a 2% linear stretch
independently on each band. The linear stretch can turn browse images over
desert areas different shades of pink/red during the heat of summer instead
of the sandy color it should be. The pink browse anomaly is only apparent
during the summer months and subsides the rest of the year. Note: the
actual data does not have this anomaly.
Q: Does red in ASTER images always represent
vegetation?
A: No, red can also indicate heat or urban areas.
Q: Why do some ASTER images have a 'smeared' line in
them?
A: These 'smears' are a result of possible instrument adjustments
while the scene was being acquired. Depending on the amount of area
affected, you might want to find an alternative scene for your study area.
Q: Why are some of the ASTER images gray?
A: When the cloud cover is so extremely saturated that it appears
in all 3 bands, an image is not viewable. As the intensity of cloud cover
may be needed data, the processing site determined it was beneficial to use
gray blocks instead of black or blank scenes.
Q: What are the Landsat MSS band designations?
A: Landsat 1,2,3 - Band 4 = green, Band 5 = red,
Band 7 = near IR. Landsat 4,5 - Band 1 = green, Band 2 = red,
Band 4 = near IR.
Q: Can an MSS image be compared to TM or ETM+ data?
A: All of this data is interchangeable, but the user would have
to watch the band designations, and adjust the resolution (i.e. increase
the pixel size) of the TM/ETM+ datasets to match the lower resolution of
the MSS data.
Q: Why do the raw browse images for Landsat 4-5 TM,
Landsat 1-5 MSS, and MRLC 1992 have different resolutions?
A: The old Landsat 4-5 TM, Landsat 1-5 MSS, and MRLC 1992 data
inventory is made up of 480-meter resolution raw browses. Currently,
the Landsat 4-5 TM data is being converted to a new media type.
During this process, 240-meter resolution raw browse image are generated.
Until the conversion is complete there will be a mixture of 240-meter
and 480-meter resolution raw browse images in the GloVis inventory.
Q: How does Landsat 7 ETM+ SLC-off data compare to
previous Landsat 7 data?
A: The center of a Landsat 7 ETM+ SLC-off scene should be
very similar in quality to previous Landsat 7 data. However, the left and
right edges of the scene will contain alternating scan lines of missing
data (Level 1G) or duplicated data (Level 0Rp or L1R). The precise location
of the affected scan lines will vary from scene to scene. It is recommended
to review the 'Show Browse' image by right-clicking on the scene in the
browse viewer and selecting 'Show Browse'. Although the 'Show Browse' image
may not show the gaps, the overlaid grid will indicate the size of the gaps
in the image. For more information, please review
http://landsat7.usgs.gov/slc_off.html.
