Landsat 7

Archive: since 1999

Landsat 7 Imagery

About Landsat 7

Involving three large American governmental organizations: NASA, NOAA and USGS launched on April 15, 1999. Landsat 7 is equipped with ETM+ (Enhanced Thematic Mapper Plus), which provides a ground survey in four modes: VNIR (Visible and Near Infrared), SWIR (Shortwave Infrared), PAN (Panchromatic - Panchromatic range), TIR (Thermal infrared - Thermal infrared range).

The Landsat 7 ETM+ instrument is designed with the significant exception of the thermal infrared band, where the ground resolution has been improved from 120 to 60 m.

The ETM instrument incorporates a new 15 m panchromatic band, as well as a 9-bit analog to digital converter. The panchromatic band was added to provide higher spatial resolution observations, as a compliment to the 30 m multispectral measurements. In order to limit the telemetered data stream to a reasonable volume, a 9-bit A-to-D system was designed so that either the upper or lower 8 bits of the radiometry could be provided from the system. This introduces the potential for two gain states (high and low), which, particularly for dark landscapes, could increase the radiometric signal.

At an altitude of 705 km, a full surface scan by Landsat 7 takes 232 turns, or 16 days. The terrain survey takes place at approximately 10 am (± 15 minutes) according to local solar time.

Landsat 7 Characteristics

Characteristic
Description
Participants
  • NASA
  • (NOAA)
  • DOI USGS
  • Spacecraft bus
  • Enhanced Thematic Mapper Plus
Launch Date
April 15, 1999
Vehicle
Delta II
Site
Western Test Range at Vandenberg Air Force Base, California
Spacecraft
  • Power provided by a single Sun-tracking solar array and two 50 Ampere-Hour (AHr), Nickel Cadmium (NiCd) batteries
  • Attitude control provided through four reaction wheels (pitch, yaw, roll, and skew); three 2-channel gyros with celestial drift updating; a static Earth sensor; a 1750 processor; and torque rods and magnetometers for momentum uploading
  • Orbit control and backup momentum unloading provided through a blow-down monopropellant hydrazine system with a single tank containing 270 pounds of hydrazine, associated plumbing, and twelve 1-pound-thrust jets
  • Weight: approx. 4,800 lbs (2,200 kg)
  • Length: 4.3 m (14 ft)
  • Diameter: 2.8 m (9 ft)
Communications
  • Direct Downlink with Solid State Recorders (SSR)
  • Data rate: 150 Mbps
Orbit
  • Worldwide Reference System-2 (WRS-2) path/row system
  • Sun-synchronous orbit at an altitude of 705 km (438 mi)
  • 233 orbit cycle; covers the entire globe every 16 days (except for the highest polar latitudes)
  • Inclined 98.2° (slightly retrograde)
  • Circles the Earth every 98.9 minutes
  • Equatorial crossing time: 10:00 a.m. +/- 15 minutes
Sensors
ETM+
Scene size
170 km x 185 km (106 mi x 115 mi)
Design life
Minimum of 5 years

Landsat 7 Specifications

Sensor Band number Band name Wavelength (μm) Resolution (m) Band Applications
ETM+ 1 Blue 0.45-0.52 30 Bathymetric mapping, distinguishing soil from vegetation, and deciduous from coniferous vegetation
ETM+ 2 Green 0.52-0.60 30 Emphasizes peak vegetation, which is useful for assessing plant vigor
ETM+ 3 Red 0.63-0.69 30 Discriminates vegetation slopes
ETM+ 4 NIR 0.77-0.90 30 Emphasizes biomass content and shorelines
ETM+ 5 SWIR 1 1.55-1.75 30 Discriminates moisture content of soil and vegetation; penetrates thin clouds
ETM+ 6 Thermal 10.40-12.50 60*(30) Thermal mapping and estimated soil moisture
ETM+ 7 SWIR 2 2.09-2.35 30 Hydrothermally altered rocks associated with mineral deposits
ETM+ 8 Panchromatic 0.52-0.90 15 15 meter resolution, sharper image definition

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