| Landsat ETM + |
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OVERVIEW |
Landsat 7, launched on April 15,1999, is the latest satellite of theLandsat program. Landsat 7's primary goal is to refresh the global archive of satellite photos, providing up-to-date and cloud free images. Although the Landsat Program is managed by NASA, data from Landsat 7 is collected and distributed by the USGS. The NASA World Wind project allows 3D images from Landsat 7 and other sources to be freely navigated and viewed from any angle.
Landsat 7 was designed to last for five years, and has the capacity to collect and transmit up to 532 images per day. It is in a polar, sun-synchronous orbit, meaning it scans across the entire earth's surface. With an altitude of 705 kilometres +/- 5 kilometres, it takes 232 orbits, or 16 days, to do so. The satellite weighs 1973 kg, is 4.04 m long, and 2.74 m in diameter. Unlike its predecessors, Landsat 7 has a solid state memory of 378 gigabits (roughly 100 images). The main instrument on board Landsat 7 is the Enhanced Thematic Mapper Plus (ETM+). |
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| Product Description |
The Landsat Enhanced Thematic Mapper Plus (ETM+) is a sensor carried onboard the Landsat 7 satellite and has acquired images of the Earth nearly continuously since July 1999, with a 16-day repeat cycle. An instrument malfunction occurred on May 31, 2003; as a result, all Landsat 7 image data acquired from July 14, 2003 (20:32:40 GMT) to the present were collected in SLC-off mode. Image data acquired from 5/31/03 (21:42:35 GMT) to 7/14/03 (20:32:40 GMT) and from 9/3/03 (01:32:15 GMT) to 9/17/03 (06:22:27 GMT) are not available for search and order.
On April 1, 2007, the Landsat 7 mission began imaging in an alternate mirror-scanning control mode from the original Scan Angle Monitor (SAM) process that has been used since the satellite was launched in 1999. This change, known as Bumper Mode, is necessary due to a predictable physical wear of the mirror bumpers mounted within the Enhanced Thematic Mapper Plus (ETM+) imaging system. Landsat 7 data users should notice little or no change as a result of this transition. Five years ago, the Landsat 5 Thematic Mapper (TM) scanner was successfully converted to this alternate imaging mode, and customers have reported no problems related to that change.
Landsat ETM+ image data consist of eight spectral bands (band designations), with a spatial resolution of 30 meters for bands 1 to 5 and band 7. Resolution for band 6 (thermal infrared) is 60 meters and resolution for band 8 (panchromatic) is 15 meters. Approximate scene size is 170 km north-south by 183 km east-west (106 mi by 114 mi).
For all Landsat 7 ETM+ data (including SLC-off products), the following levels of correction are available to the general public. |
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| Raw Uncorrected (Level 0Rp) (SLC-on and SLC-off) |
| The Level 0Rp (L0Rp) data product provides reformatted raw data with no radiometric or geometric correction applied. Reformatting includes shifting pixels by integer amounts to account for 1) the alternating forward-reverse scanning pattern of the sensor, 2) the odd-even detector arrangement within each band, and 3) the detector offsets inherent to the focal plane array engineering design. The pixels are NOT aligned per scan line. Image data are stored as 8-bit unsigned integer (DN) values. Raw uncorrected (L0Rp) data are processed through the Landsat Archive Manager (LAM) and will have no map projection or datum assigned. L0Rp data are in HDF format and distributed on CD, DVD, or via FTP download. The SLC-off product includes the original duplicated scan lines along the edge of the scene.
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| Radiometric Corrected (Level 1R) (SLC-on and SLC-off) |
| The Level 1R (L1R) data product provides radiometrically corrected L0R data where calibration is applied, but geometric correction is not applied. Scan lines are reversed, but the pixels are NOT aligned per scan line. Image data are not geometrically corrected or geographically referenced and are provided in 16-bit radiance) values. All Level 1R products are processed by the Level 1 Product Generation System (
LPGS
).
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| Systematic Correction (Level 1G) (SLC-on and SLC-off) |
| The Level 1G (L1G) data product provides systematic radiometric and geometric accuracy, which is derived from data collected by the sensor and spacecraft. The scene will be rotated, aligned, and georeferenced to a user-specified map projection. Geometric accuracy of the systematically corrected product should be within 250 meters (1 sigma) for low-relief areas at sea level. The SLC-off product includes the original data gaps. Duplicated pixels have been replaced with null values (zero-fill) and the image therefore contains alternating "stripes" of missing data. A scan gap mask is included with the final product. Please click
here
for more information on SLC-off Level 1G data. Level 1G SLC-on products are processed by the Level 1 Product Generation System (
LPGS
) or the National Land Archive Production System (
NLAPS
). Level 1G SLC-off products are processed by the Level 1 Product Generation System (
LPGS
).
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| Gap-filled (Level 1G) (SLC-off only) |
| A gap-filled SLC-off product is a derived product in which all missing image pixels in the original SLC-off image have been replaced with estimated values based on one or more histogram-matched scene(s) from a previous date. The primary (SLC-off) and fill (SLC-off and/or SLC-on) scenes are radiometrically and geometrically corrected using the satellite model and platform/ephemeris information. All images are rotated and aligned to the user-specified map projection. The primary scene is co-registered to the fill scene(s) and all missing image pixels in the primary scene are then replaced with estimated values based on local linear histogram-matched data from the fill scene(s). A scan gap mask is generated for each band of the primary scene, which identifies the original data source for every pixel within the final output product. The delivered data product consists of the final gap-filled image, along with a gap mask (one file per band). For more information on gap-filled products and processing see the
Landsat 7 SLC-off gap-filled product description
. A scan gap mask is included with the final product (
Detailed Description
). Level 1 SLC-off gap-filled products are processed by the Level 1 Product Generation System (
LPGS
).
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| Ordering Parameters |
Options (NLAPS) SLC-on Only |
Options (LPGS) |
| Map projection |
UTM
SOM-B
ALBERS
other* |
UTM
SOM-B
ALBERS
LCC
PS
PC
TM
OMA
OMB |
| Horizontal datum |
WGS84
NAD83
NAD27
other* |
WGS84 |
| Resampling method |
CC (Cubic Convolution)
NN (Nearest Neighbor)
MTF (Modulation Transfer Function)
other* |
CC (Cubic Convolution)
NN (Nearest Neighbor)
MTF (Modulation Transfer Function) |
Scan gap interpolation
(SLC-off only) |
0 to 15 pixels (default = 2 pixels) |
0 to 15 pixels (default = 2 pixels)
|
Scan gap interpolation
(SLC-off Gap filled only) |
Not Available |
Default only (0 pixels) |
| Image Orientation |
Map (north up)
Path (satellite/nominal)
other* |
Map (north up)
Path (satellite/nominal) |
| Pixel size |
30 meter (30m/15m/60m)
28.5 meter (28.5m/14.25m/57m)
25 meter (25m/12.5m/50m)
other* |
30 meter (30m/15m/60m)
28.5 meter (28.5m/14.25m/57m)
25 meter (25m/25m/50m)
other* |
| Format |
GeoTIFF
NDF (NLAPS Data Format)
Fast L7
HDF (Hierarchical Data Format, v4.1) |
GeoTIFF
HDF (Heirarchical Data Format, v4.1)
Fast L7 |
| Media Type |
CD
DVD
FTP |
CD
DVD
FTP |
| Delivery Times |
FTP: 1 to 3 days
Media: 5 to 10 days
The above are average delivery times and are not guaranteed. The actual delivery time may vary, depending on the workload at the time an order is placed. Delivery time may also be longer if shipping to a location outside the United States. |
FTP: 1 to 3 days
Media: 5 to 10 days
The above are average delivery times and are not guaranteed. The actual delivery time may vary, depending on the workload at the time an order is placed. Delivery time may also be longer if shipping to a location outside the United States. |
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