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A scatterometer is used to determine the normalized radar cross section of a surface.  They use microwave pulses to measure reflected energy.  It also measures noise to determine backscattering.  Scatterometers are mostly used to measure near surface winds over the ocean and is useful in the study of vegetation, soil moisture, polar ice and global change.  The first one was launched with the QuikSCAT satellite in 1999 and one is being used on the SAC-D satellite to reduce noise for the Aquarious instrument on board to study sea surface salinity. 

Reference: NASA WINDS

[Added by Wade Paxson 5/2/10]


The Scanning Imaging Absorption SpectroMeter for Atmospheric CartograpHY (SCIAMACHY) is an instrument onboard the ESA ENVISAT platform (launched March 2002). The primary mission of SCIAMACHY is to measure trace gases in the troposphere and stratosphere. The instrument uses passive remote sensing techniques to monitor backscattered, reflected, transmitted, or emitted radiation from the atmosphere and Earth’s surface using a spectrometer that boasts a wavelength range between 240 and 2380 nm. The instrument can operate with relatively high resolution between 0.2 nm to 1.5 nm in the ranges of 240 nm to 1700 nm and 2.0 um to 2.38 um.

(Image source:
1 ESA SCIAMACY homepage:
2 Book published highlighting SCIAMACY’s successes:
3 Product data access site:
(added by Perry Edwards, May 1, 2010)


The Sea-viewing Wide Field-of-view Sensor (SeaWIFS) is a multi-spectral imaging instrument onboard GeoEye’s OrbView-2 (SeaStar) satellite and is part of the NASA EOS Mission. The satellite (and instrument) has been fully operational since September 18, 1997, operating in a sun-synchronous orbit and can provide single day near complete global coverage.
SeaWiFS has 8 optical bands in the visible (20 nm bandwidth) and near-infrared (40 nm bandwidth) with a minimum spatial resolution of 1.1 km. The optical bands are:
1. 402-422 nm
2. 433-453 nm
3. 480-500 nm
4. 500-520 nm
5. 545-565 nm
6. 660-680 nm
7. 745-785 nm
8. 845-885 nm
SeaWiFS is exclusively used to monitor ocean characteristics through such as sea surface temperature (SST), water clarity, and chlorophyll-a concentration.

(Image source:
1 NASA SeaWiFS project page:
2 Nasa EOS SeaWiFS page:
(added by Perry Edwards, May 1, 2010)


SETI is the Search for Extra-Terrestrial Intelligence program. SETI is an exploratory science that seeks evidence of life in the universe by looking for some signature of its technology. There have been many theories of how to search for extra-terrestrial life, such as passive radars, radio wave transmission, lasers, and IR detectors.

Tarter, Jill. "The Center for SETI Research". Accessed 04/12/2010.

Signal to Noise Ratio

It is the measure to quantify how much a signal has been affected (or attenuated) by noise. In practice it is nothing but the ratio of the power of a signal to the power of the noise accompanying it.

Signal to noise ratio is expressed in three forms:

  • In terms of its power: SNR = Power(Signal)/Power(Noise)
  • In terms of amplitude: SNR = Amplitude^2 (Signal)/Amplitude^2(Noise)
  • In terms of a distribution: SNR = Mean/Standard Deviation (Commonly used in imaging techniques)

We can also define it in terms of decibels (dB) where each of the above entries are operated by 10*log (X) where X are the above SNRs.

[Added by Udit Narayanan on 05/01/2010]

Solid Angle

Solid angle is a two dimensional measurement of three dimensional space. It is commonly used to describe how large an object appears to an observer from a specified point. For instance, a small object close to an observer can appear to be the same size as a larger object farther away. An example of this is the sun and moon which appear to be about the same size when viewed from Earth; however, the sun is much larger than the moon. The units for solid angle is steradians (sr) and there is 4pi sr in a sphere.  Solid angle is a strong function of the distance between the observer and the object.

Solid Angle in remote sensing is often used to describe a sensor’s footprint. The solid angle would be the area subtended by the satellites Field of View.

The red area is the Solid Angle



added by M. Rydzik on 03/26/2010

South Atlantic Anomaly

The South Atlantic Anomaly (SAA) is an area, where the geomagnetic field strength is less than the ambient field strength. This phenomenon allows for cosmic rays and high energetic protons to enter the atmosphere at much lower altitudes. Added by Adam on 04/20/2010

The South Atlantic Anomaly is pictured in red.

Arida, Michael. "South Atlantic Anomaly". NASA GSFC., accessed on 04/20/2010.

Spectral Resolution

The spectral resolution or resolving power of a remote sensing platform is a measure of its power to distinguish between features in the electromagnetic spectrum.  It can be calculated using the following equation,

where lambda is the wavelength and delta lambda is the smallest resolvable wavelenth.

Spectral resolution can also be defined as the width of spectral bands.  For multispectral imaging systems the width of each of the several bands defines the spectral resolution.


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[added by Jeff Eveland on 05/01/2010]


Starlette and Stella satellites - satellites launched by the French in 1975 and 1995.  The size of Starlette and Stelle are relatively small in size compared to other satellites.  This feature heightens their sensitivity to gravity.  Their main purpose is for gravity field recovery. added by Shelly on 5/3/2010


Swath Width

Swath width is the cross-track width of an image collected by a satellite.  The swath width is measured perpendicularly to the longitudinal extent of the swath, which is defined by the motion of the satellite with respect to the surface of the Earth.  Together the swath width and longitudinal extent define the area of a scene.

Figure: Swath width for a scene taken by MOS-1


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[added by Jeff Eveland on 05/02/2010]


The Swift satellite was deployed on November 20, 2004 to study deep space gamma-ray bursts (GRB) and is part of NASA’s medium explorer (MIDEX) program. The main mission objectives of Swift are (from NASA Swift website):
-to determine the origin of GRBs
-classify GRBs and search for new types
-determine how the blast wave evolves and interacts with the surroundings
-use GRBs to study the early universe
-perform a sensitive survey of the sky in the hard X-ray band

Swift has three primary instruments on board to detect, observe and measure GRBs: the Burst Alert Telescope, the X-Ray Telescope, and the UV/Optical Telescope. The name for “Swift” comes from the idea that the satellite will “swiftly” change its’ instrument pointing direction to observe GRBs once detected by the Burst Alert Telescope. GRBs can occur on the order of a few milliseconds to several hundred seconds. The Mission Operations Center for Swift is located at PENN STATE UNIVERSITY and provides full command and control of the spacecraft.

For more information on Swift, check out the Swift fact sheet and the references below:

1 Swift fact sheet:
2 NASA Swift homepage:
3 Penn State’s Swift homepage:

(added by Perry Edwards, May 2, 2010)

Synthetic Aperture Radar (SAR)

A type of radar that uses multiple radar returns in order to produce higher-resolution images than can be obtained by traditional radar. Ground based SAR usually consists of multiple antennas separated by some distance while SAR on a moving platform consists of a single antenna. This technique allows for the use of a smaller antenna than would be commonly needed to obtain the same resolution. In order to produced a SAR image it must be post processed using high performance computers which must account for both the amplitude and phase of the returned pulse. The movement of the platform also complicates the processing, therefore it is critical to have accurate pith, roll, and yaw information of the platform. One product of SAR is digital elevation maps.

A diagram SAR aboard an aircraft



added by M. Rydzik on 01/31/2010

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