National Archives of Satellite Images: Landsat satellites

The Landsat program was created in the United States. In 1965 the U. S. Geological Survey (USGS) proposed the idea of a remote sensing satellite program to gather facts about the natural resources of the Earth.

The first satellite of the Landsat series was sent into the air in July of 1972. Seven satellites mark the Landsat series, although Landsat 6 was unsuccessful. The Landsat-1 satellite was a milestone in the history of remote sensing, since its images formed the basis of satellite imaging in modern resources research and also were used to create the first satellite image maps.

Of the six successfully implemented Landsat Satellites, only Landsat 5 and 7 remain in operation. The Landsat-1 took images from July, 1972 until January, 1978, the Landsat-2 from 1975 until 1982 and the Landsat-3 from March, 1978 until March, 1983.

The Landsat-MSS sensor has 4 spectral channels in the visible and infrared spectrums with a resolution of 80 m. The reception of the MSS images was discontinued in 1993. The Landsat TM images have been used since 1984. It has 6 spectral channels, with 30 m resolution in the visible and infrared spectrums. The sixth channel is the thermal channel, with a resolution of 120 m.

Launching date of Landsat satellites and proposed launching of LDCM:

Technical features of Landsat 5 and Landsat 7:

Launching date: 1984 (TM5), 1999 (TM7)
Height: 705,3 km
Orbit: circular, sun-synchronous, near-polar orbit, provide full coverage between 81° North and 81° South.
Equatorial crossing: 9.30 - 10.00 a.m. (descending)
Repeat cycle: 16 days (8 - 8 days)
Inclination: 98.2°
Track width: 183 km
Cartographical accuracy: 12 m

Multi Spectral Scanner and Thematic Mapper:

MSS and RBV:

Landsat 1, 2 and 3 carried the MSS instrument and RBV (Return Beam Vidicon) camera system. The RBV was supposed to be the prime instrument, but the data from the MSS instrument was later found to be superior. In addition, the RBV instrument caused an electrical transit that resulted in the satellite briefly losing altitude control. The MSS recorded data in 4 spectral bands: a green, red and two infrared bands. The MSS had been used for collecting data from 1972 until 1993 when in was turned off.

TM:

In addition to the MSS, Landsat 4 and 5 carried a sensor called the Thematic Mapper which improved spectral and spatial resolution which increased the portion of the electromagnetic spectrum detected and also the detail of the images taken of the ground. The Landsat 4 TM had 7 spectral bands and included thermal and infrared portions of the electromagnetic spectrum.

Spectral bands of Landsat 5 and 7:

LDCM

Landsat Data Community Mission is to be launched by the end of 2010. It will provide moderate resolution (15 – 100 m, depending on spectral frequency) measurements of the Earth’s terrestrial and polar regions in the visible, near-infrared, short wave infrared and thermal infrared ranges. The LDCM satellite carries two science instruments: the OLI (Operational Land Imager) and the TIRS (Thermal Infrared Sensor).

The TIRS will collect data for two more narrow spectral bands in the thermal region formerly covered by one wide spectral band on Landsats 4–7.

The OLI provides two new spectral bands; one is tailored especially for detecting cirrus clouds and the other is for coastal zone observations. OLI will collect data for visible, near infrared, and short wave infrared spectral bands as well as a panchromatic band. In addition, two new bands will be established: a coastal band and a cirrus band. The heritage Landsat multispectral bands will also be included in the OLI. Additionally, the bandwidth has been refined for six of the heritage bands

http://landsat.gsfc.nasa.gov/about/ldcm.html

Additional information:

The era of privatization

In 1984, when Landsat 5 was launched, the American Congress decided land satellites could be privatized. The NOAA (National Oceanic and Atmospheric Administration) which was charged with operation of the weather satellites was instructed to find a commercial vendor for Landsat data. It selected the EOSAT (Earth Observation Satellite Company) which limited commercial freedom and raised the prices of images. As a result, many data users migrated to the free low-resolution land data being captured by meteorological satellites. Finally, in 1986 the SPOT, a French Landsat-like satellite launch broke the U.S. monopoly. Many observations from 1984 – 1999 were missed because there were no obvious and immediate buyers for satellite data. By 1989 the NOAA directed EOSA to turn off the satellites. The program was only saved by a strong protest from Congress and an intervention by the Vice President.  By 2001 operational control was officially returned to the Federal government. After the failed launch of Landsat 6 in 1993 the data gap seemed to be eminent until the government-owned Landsat 7 was successfully launched in 1999.

The excellent data quality, consistent global archiving scheme and reduced pricing of Landsat 7 led to a large increase in the number of Landsat data users.

SLC-off mode:

The Landsat mission proceeded flawlessly until May 2003 when a hardware component (SLC) failure left wedge-shaped spaces of missing data on either side of Landsat 7’s images. In this SLC (Scan Line Corrector) mode the ETM+ still acquires approximately 75% of the data for any given scene. To fulfill the expectations of the users for full coverage single scenes, data from multiple acquisitions are being merged to resolve the SCL-off data gaps. A binary bit mask is provided so that the users can determine where the data from any given pixel originated.