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-1A VNIR and TIR
The ASTER L1A VNIR (Level-1A Visible Near Infra-Red) browse images
are displayed as a 3N, 2,1 (RGB) color composite.
The ASTER L1A TIR (Level-1A 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.
GloVis provides a catalog of ASTER Level-1A browse images (VNIR
for daytime scenes and TIR for nighttime scenes) for the entire
world. The following two data sets are orderable from GloVis:
ASTER Level-1A (
http://lpdaac.usgs.gov/aster/ast_l1a.asp) contains
reconstructed, unprocessed instrument digital numbers (DNs) derived
from the telemetry streams of the 3 telescopes: Visible Near
Infrared (VNIR), Shortwave Infrared (SWIR), and Thermal Infrared
(TIR).
ASTER Level-1B (
http://lpdaac.usgs.gov/aster/ast_l1b.asp) 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.
EO-1 ALI
The Advanced Land Imager (ALI) browse images are generated from the
Level 1 radiometrically corrected data and displayed as a 5,4,2
(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.
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.
Pixels are subsampled to a resolution of 180 meters from the
original 30-meter data.
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.
When ordering this data, a Warning Box will pop up reminding the
user they are attempting to order SLC-off 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
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 4-7 Combined
This dataset contains images from Landsat ETM+, Landsat ETM+
SLC-off, Landsat TM, and Landsat 4 - 5 MSS. These are all the
Landsat sensors that utilize WRS-2. To allow for
easy browsing through the various datasets, the scenes are merged
together in chronological order. This allows the scenes to be
searched, browsed, and ordered as a single dataset.
The selected image is outlined by a unique color based on
its corresponding dataset. This allows users to easily
distinguish between images of different datasets.
Dataset
Color
Landsat ETM+
Blue
Landsat ETM+ SLC-off
Green
Landsat TM
Yellow
Landsat 4 - 5 MSS
Red
Due the to large size of the combined datasets, loading the
inventory will be very time consuming when using dialup internet or
other slow connections.
For details on the individual sensors that make up this
combined dataset, please refer to the specific sensor information
above.
When scenes are added to the combined dataset scene list, the
scene will also be added to the scene list for that corresponding
sensor. Likewise, when working with a single sensor, adding
scenes to the scene list will be reflected in the combined
dataset scene list. All other scene list features will be
handled in the same manner.
Landsat Orthorectified ETM+
The Landsat Orthorectified ETM+ and 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.
Full-resolution data may be downloaded for free.
Landsat Orthorectified Pansharpened
ETM+
The Landsat Orthorectified PansharpenedETM+ and 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.
Full-resolution data may be downloaded for free.
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.
Full-resolution data may be downloaded for free.
Landsat Orthorectified MSS
The Orthorectified MSS browse images are displayed as a 4,2,1 (RGB)
color composite for Landsats 4 - 5 MSS, 7,5,4 (R,G,B) for Landsats
1 - 3 MSS.
Landsats 1-3 MSS data provide worldwide historical coverage.
Landsats 4-5 MSS data is more sparse, and used only to fill in gaps
in coverage.
Pixels are subsampled to a resolution of 480 meters from the
original 80-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.
Full-resolution data may be downloaded for free.
MODIS
The images are displayed as a 1,4,3 (RGB).
The images generally cover a 10° x 10° area.
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.
Full-resolution MRLC 2001 Terrain Corrected data may be downloaded
for free.
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.
National Aerial Photography Program (NAPP)
NAPP browse images are created from medium resolution digital
products that are captured by a digital camera. The browse files
are resampled to 72 dpi.
NAPP scenes cover approximately a 5.5 x 5.5 mile area.
NAPP browse on GloVis have been clipped to remove the excess film
margins and the images have been oriented "north up".
Some browse may contain the Moiré pattern artifact.
The Moiré pattern artifact is a pattern in areas where
the spatial frequency of the land area is higher than detector
density on the focal plane in the digital camera used to
capture the image. The artifact that results is a type of
aliasing known as moiré patterns or moiré waves.
This well-known artifact is not an error in the original film
or the digitizing process. The moiré pattern shown in
some of the browse is not present when scanned at
high-resolution on photogrammetric quality scanners used at the
Center for Earth Resources Observation and Sciences. For more
information on this artifact, check these web sites:
http://www.dpreview.com/learn/?/Glossary/Digital_Imaging/Moire_01.htm
http://www.maxim-ic.com/appnotes.cfm/appnote_number/928
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 4-5 TM browse so dark and low
contrast?
A: Differences in the browse generation algorithms used to create
the Landsat 7 ETM+ and the Landsat 4-5 TM browse result in the TM browse
being sometimes significantly darker and lower contrast than similar
scenes in the ETM+ inventory over the same geographic region. The
differences in the browse generation algorithms have been identified and
changes to the Landsat TM browse generation algorithm are scheduled.
These changes will correct differences in the specifics of the method
used to histogram the data before processing the contrast stretch,
bringing the two algorithms closer together so the browse generated
by each will be visually more similar in brightness and contrast.
The changes to the Landsat TM browse generation algorithm are scheduled
for release in early March, 2005, but that will only affect the new browse
being created from that date forward. There currently is not a
reprocessing plan to address the dark browse in the current TM inventory.
Until the new algorithm is in place and all the current browse have been
reprocessed with the new algorithm, the Landsat 4-5 TM browse inventory
contains a number of browse that don't reflect the true brightness and
contrast of the scene data. We do not have a method to identify the exact
scenes that are affected by the algorithm deficiencies, so there is no way
for us to indicate for the users which browse have this "too dark" issue.
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 USGS EROS. These scenes may still be available from other
International Ground
Stations. Please note that this data is not a product of USGS EROS, 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: Red color in the VNIR images generally represent vegetation.
Q: Why do some ASTER images have a 'smeared' line in
them?
A: Images with smeared lines generally indicate a temporary
detector-related problem during the course of acquisition. They are
infrequent and irreversible. They generally result in a data gap on the
image. Depending on the amount of area affected and your application needs,
you may want to find an alternative scene.
Q: Why are some ASTER images completely white?
A: Completely white, or nearly completely white, browse images
exist because saturated cloud cover leaves little to no useful image data.
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'. For more information, please
review
http://landsat.usgs.gov/slc_off.html.
Q: Why does the EO-1 Scene ID list a path and row that
is different than the path and row of the center part of the image?
A: EO-1 imagery is collected based on a targeted center point. The
path and row listed in the Scene ID represents when the EO-1 instruments
began imaging, even though the target point may fall in the next row. In
the diagram below, the coordinates for Target 2 fall within the WRS row
below that of the coordinates for Target 1. However, since the instruments
began imaging Target 1 and Target 2 in the same path/row, both images would
have the same Target WRS path and Target WRS row in the
Scene ID. EO-1 is not able to image both targets on the same date;
therefore, the difference in the Scene IDs would show up in the Julian day
of acquisition.
Q: Why can't I search for ASTER LIB data on GloVis?
A: Effective May 24, 2006, only ASTER LIA data will be searchable
on GloVis. However, should a user select and order a scene, a drop-down
option will allow the user to change the data request to LIB. (LIB
products will only be produced on-demand.) Note: ASTER data can only be
ordered FTP-Pull, it is no longer available on media.
Q: Why are some ASTER L1A images missing? I was able to
find them when they were L1B, but not as L1A images.
A: GloVis displays the inventory of ASTER L1A images supplied by
the LP DAAC. GloVis does not have the full ASTER L1A inventory since there
are a large number of older granules that have extremely low resolution
browse that are too small to be useful in GloVis. So, those older granules
(from before September 2003) have not been made available to GloVis at this
point.
The LP DAAC is reprocessing the granules in question to create the modern
browse. As the browse images are created and provided to GloVis, the
granules will be displayed. Until the full inventory is supplied, it might
be necessary for users to use the EDG (
http://edcimswww.cr.usgs.gov/pub/imswelcome/) to find the older data.
Q: Can I find the actual gain and bias values for a
Landsat scene on GloVis?
A: No, you will not find the actual gain and bias values on GloVis.
Gain and bias values can only be obtained when actual data is ordered
because to gain and bias values are only available in the final product
metadata. These coefficients can then be applied with the DN values within
the imagery to convert to accurate radiance values.
For information on gain and bias values, go to this site.
Q: If NAPP scenes cover a square area, why do they
appear rectangular in GloVis?
A: NAPP browse images are provided in a geographic projection with
pixels that are not square in geographic coordinates. To be properly
displayed in GloVis, the browse images are resized to make the pixels
square in geographic coordinates. The result is that the browse images
end up being rectangular.
