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The Landsat Program

The Landsat program has been acquiring remote images of Earth since 1972 and continues today with Landsat 7 (ETM+). This program has provided nearly 40 years of continuous observation of our planet! Landsat 4, 5, and 7 have many of the same spectral channels, thus we have continuous data from 1982 - present for consistent detection of land change.

Over the past several years there were questions as to whether or not the Landsat program would/should continue. Currently there are plans to continue the program with the Landsat Data Continuity Mission (LDCM), which is scheduled to launch in Dec. 2012.

Landsat 1: 1972-1978

! This satellite carried 2 science instruments, a camera and the highly experimental Multispectral Scanner (MSS) instrument. The MSS had 4 spectral bands (red, green, and two infrared bands) and proved to be a huge success. This satellite was originally known as the Earth Resources Technology Satellite (ERTS). Former director of the USGS once stated that "The ERTS spacecraft represent the first step in merging space and remote-sensing technologies into a system for inventorying and managing the Earth's resources."

Landsat 2: 1975-1982

! Very similar to the ERTS (Landsat 1); instruments included a camera and MSS.

Landsat 3: 1978-1983

! Also contained camera and MSS, but this version of MSS had a 5th (thermal) band. The thermal band failed early in the mission. At this point, some of the responsibility of the Landsat program was shifted from NASA to NOAA.

Landsat 4: 1982-2001

! A big change from earlier Landsats, the 4th one in the series no longer had a ‘camera’, but instead had the MSS instrument and a new instrument....the Thematic Mapper (TM). The TM instrument had 7 spectral bands (red, green, blue, near-IR, 2 mid-IR bands, and a thermal band). This mission was plagued with difficulties regarding downlinking/transmitting of data and ultimately data downlink stopped in 1993. Also, part of the operations were transferred to USGS and the private sector.

Landsat 5: 1984 - present

! Same payload (instruments) as Landsat 4. A transmitter failed in 1987 and made data downlink impossible for many regions of the planet (outside of range of U.S. data receivers). The MSS was turned off in 1995, but the TM instrument still operates. During this time period much of the program was privatized, which led to a number of difficulties (data prices increased by 600%, data acquisition and archiving decreased due to lack of

buyers, calibration and characterization of the instruments lapsed). In 1989, many of these issues and other factors led the government to turn off the satellites and cancel the Landsat program. There was a large outcry by the public and data users and this caused Congress to demand that a government-owned Landsat 7 satellite be flown. Operation of Landsat 4 and 5 was also returned to the government. This also allowed all Landsat 4 & 5 data to be sold to the public at standard USGS prices.

Landsat 6: 1993, failed on launch

! This satellite was launched during the period of Landsat privatization and failed because it did not reach velocity to obtain orbit. This satellite carried the Enhanced Thematic Mapper (ETM) instrument, which had the same 7 bands as the TM instrument plus an 8th, broad band at visible wavelengths with higher spatial resolution (15 m/pixel).

Landsat 7: 1999 - present

The Landsat 7 satellite carries the Enhanced Thematic Mapper Plus (ETM+) instrument. This instrument has the same capabilities as the TM instruments on Landsat 4 & 5 with some additional benefits: the 15 m/pixel panchromatic band (was also on the failed Landsat 6), on-board calibration features to ensure good radiance values, a thermal IR band with 60 m/pixel resolution, an on-board data recorder (for storing data in case it can’t be downlinked right away). In 2008 the USGS made all Landsat 7 data free to the public, and in 2009 all Landsat data became freely available. In 2003 there was a hardware failure that resulted in partial data loss for each image (only about 75% of an image is accurately acquired), but the instrument still operates today and provides some of the best-calibrated data of Earth.

Landsat Data Continuity Mission (LDCM): scheduled to launch in December 2012

This upcoming mission will continue the Landsat program and allow continuous monitoring of surface and atmospheric conditions. It will have 2 instruments: the Operational Land Imager (OLI) for visible and near-infrared channels, which is the counterpart to the ETM+ instrument on Landsat 7, and the Thermal Instrument (TIRS).

The OLI instrument will have 2 ‘new’ bands compared to the ETM+ instrument. These include a ‘coastal’ band at very short wavelengths and a ‘cirrus’ (atmospheric) band near ~1400 nm...note that the latter is NOT in an atmospheric window!

Advanced Very High Resolution Radiometer (AVHRR)

The AVHRR instrument has been flown on several NOAA satellites and the most recent version of the instrument has 6 channels (see chart below). The latest version (AVHRR/3) is on the NOAA-15 satellite that was launched in 1998. NOAA has a minimum of two satellites observing the planet at all times, and these satellites utilize the AVHRR instrument. These satellites are primarily for meteorological purposes, as evident from the ‘use’ listed in the chart below. However, note that there are channels in both the visible and near-infrared....therefore you can use AVHRR data to calculate NDVI and monitor changes in vegetation patterns!

The first AVHRR instrument was launched in 1978. Therefore, although the spatial resolution is relatively coarse, these data provide a continuous view of the surface to examine changes over the past 30+ years.

AVHRR data continue to be an important resource for scientific studies, but the advent of the MODIS instruments/data are now playing a bigger role because of the increased spectral and spatial resolution. Recall that MODIS instruments are operated on NASA missions, whereas AVHRR instruments are on NOAA missions.

AVHRR/3 Channel CharacteristicsAVHRR/3 Channel CharacteristicsAVHRR/3 Channel CharacteristicsAVHRR/3 Channel Characteristics

Channel Number

Resolution at Nadir

Wavelength (um) Typical Use

1 1.09 km 0.58 - 0.68 Daytime cloud and surface mapping

2 1.09 km 0.725 - 1.00 Land-water boundaries

3A 1.09 km 1.58 - 1.64 Snow and ice detection

3B 1.09 km 3.55 - 3.93 Night cloud mapping, sea surface temperature

4 1.09 km 10.30 - 11.30 Night cloud mapping, sea surface temperature

5 1.09 km 11.50 - 12.50 Sea surface temperature

AVHRR imagemosaic of the U.S.

AVHRR map of global sea surface temperature (October, 2001).

The Earth Observing System (EOS)

EOS is a scientific program operated by NASA that consists of numerous satellites.From the NASA webpage:

The Earth Observing System (EOS) is a coordinated series of polar-orbiting and low inclination satellites for long-term global observations of the land surface, biosphere, solid Earth, atmosphere, and oceans. EOS is a major component of the Earth Science Division of NASA's Science Mission Directorate. EOS enables an improved understanding of the Earth as an integrated system. The EOS Project Science Office (EOSPSO) is committed to bringing program information and resources to program scientists and the general public alike.

The following page has a list of satellites/missions that are part of the EOS program. Note that Landsat 7 is part of this list. Terra is considered to be a flagship mission in the EOS program. The Terra satellite flies north to south and passes over the equator in the morning, whereas Aqua flies south to north and passes the equator in the afternoon.

Terra (EOS AM satellite)

Launched in 1999 and still operating today.This mission has the following instruments:

ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer)MODIS (Moderate-Resolution Imaging Spectrometer)MISR (Multiangle Imaging Spectroradiometer)MOPITT (Measurements of Pollution in the Troposphere)CERES (Clouds and Earth’s Radiant Energy System)

Aqua (EOS PM satellite)

Launched in 2002 and still operating today.This mission has the following instruments:

MODIS (Moderate-Resolution Imaging Spectrometer)CERES (Clouds and Earth’s Radiant Energy System)AIRS (Atmospheric Infrared Sounder)AMSR-E (Advanced Microwave Scanning Radiometer for the EOS)AMSU-A (Advanced Microwave Sounding Unit-A)HSB (Humidity Sounder for Brazil)

EOS

Active:

Landsat 7 April 15, 1999

Quik Scatterometer (QuikSCAT) June 19, 1999

Terra December 18, 1999

Active Cavity Radiometer Irradiance Monitor Satellite (ACRIMSAT) December 20, 1999

Jason-1 December 7, 2001

Aqua May 4, 2002

Solar Radiation and Climate Experiment (SORCE) January 25, 2003

Aura July 15, 2004

Ocean Surface Topography Mission (OSTM) June 20, 2008

Future:

Landsat Data Continuity Mission (LDCM) December 2012

Completed:

Upper Atmosphere Research Satellite (UARS) September 12, 1991

ATLAS March 24, 1992

TOPEX/Poseidon August 10, 1992

Spaceborne Imaging Radar-C (SIR-C) April 19, 1994

Radar Satellite (RADARSAT) November 4, 1995

Total Ozone Mapping Spectrometer-Earth Probe (TOMS-EP) July 2, 1996

Advanced Earth Observing Satellite (ADEOS) August 17, 1996

Orbview-2/SeaWiFS August 1, 1997

Tomographic Experiment using Radiative Recombinative Ionospheric EUV and Radio Sources (TERRIERS) May 18, 1999

Shuttle Radar Topography Mission (SRTM) February 11, 2000

Challenging Mini-Satellite Payload (CHAMP) July 15, 2000

Stratospheric Aerosol and Gas Experiment (SAGE III) December 10, 2001

SeaWinds (ADEOS II) December 14, 2002

Ice, Cloud, and land Elevation Satellite (ICESat) January 12, 2003

Missions for Ocean Surface TopographyUnderstanding variations in the surface topography of the oceans is important for tracking El Niño / La Niña trends and for incorporating into models to understand ocean circulation patterns.

Several past/current/upcoming missions include:

TOPEX/Poseidon (1992-2006) - global mapping of seasonal cycles and other variations in the ocean; critical for testing ocean circulation models!

Jason-1 (2001 - present) - carries updated versions of instruments on Poseidon.

OSTM/Jason-2 (2008 - present) - continuation of the ‘Jason’ missions for monitoring changes in sea height and testing ocean circulation models.

Jason-3 (anticipated launch 2014)

GRACE (launch 2002) - This is the Gravity Recovery and Climate Experiment and consists of 2 spacecraft flying 220 km apart. This mission provides continuous mapping of the geoid (a hypothetical surface that coincides with mean sea level). The gravity field is perpendicular to the geoid.

Global sea level has risen about 2.85 millimeters (0.1 inch) a year since Topex/Poseidon (on the left) began its precise measurement of sea surface height in 1993 and was followed by Jason-1 in 2001. In this graph, the vertical scale represents globally averaged sea level. Seasonal variations in sea level have been removed to show the underlying trend. Image credit: University of Colorado

Every 10 days, Jason-1 measures the height of more than 90% of the world's ice-free ocean with its radar altimeter and completes 127 revolutions, or orbits, around Earth.To measure sea surface height it is necessary to know satellite's exact position in its orbit and the distance between the satellite and the ocean's surface. Corrections are made for variable amounts of water vapor in the lower atmosphere and free electrons in the upper atmosphere, which can delay the altimeter's microwave pulses. The sea height caused by gravity (the geoid) is mathematically removed in order to create maps of ocean surface topography.

The GRACE mission detects changes in Earth's gravity field by monitoring the changes in distance between the two satellites as they orbit Earth. The drawing is not to scale; the trailing spacecraft would actually be about 220 kilometers behind the lead spacecraft. The figure on the right shows a gravity map derived from GRACE data.

The figure above shows an estimate of the change in ice mass for the Greenland ice sheet, as determined from GRACE data.