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Earth Imaging Glossary
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HASSELBLAD 500 EL/M 70-MM CAMERAS
NASA has modified standard off-the-shelf Hasselblad 70 mm cameras to operate in zero
gravity aboard the Space Shuttle. A data recording module (DRM) has also been installed on
each camera to record the date, time (Greenwich Mean Time), mission number, roll number,
and frame number. The cameras utilize a 70 mm film format and operate with one of three
lenses (50, 100, or 250 mm) to acquire high quality photographs through four viewing ports
on the Shuttle.
HDT--High Density Tapes
HDTs are high density (high capacity) magnetic tapes.
HORIZONTAL INTEGRATION
The process of mosaicking adjacent parts of a map or image together into a single map or
image. This process might require geometric adjustments to the image itself or the features
within it so that matching occurs across mosaic seams.
HORIZONTAL POLARIZATION
Transmission of microwaves so that the electric lines of force are horizontal, while the
magnetic lines of force are vertical.
HORIZONTAL POSITIONAL ACCURACY
Horizontal positional accuracy is based upon the use of USGS source quadrangles which are
compiled to meet National Map Accuracy Standards (NMAS). NMAS horizontal accuracy
requires that at least 90 percent of points tested are within 0.02 inches of the true position.
The digital data are estimated to contain a horizontal positional error of less than or equal to
0.003 inches standard error in the two component directions relative to the source
quadrangle.
HRPT--High Resolution Picture Transmission
HRPT data are full resolution image data transmitted to a ground station as they are
collected. The average instantaneous field-of-view of 1.4 milliradians yields a HRPT ground
resolution of approximately 1.1 km at the satellite nadir from the nominal orbit altitude of
833 km (517 mi).
HRV--High Resolution Visible Imaging Instrument
The HRV instrument is a multispectral radiometer designed for SPOT spacecraft. The HRV
instrument provides for high-resolution imaging in the visible and near-infrared portions of
the electromagnetic spectrum. The first three SPOT satellites carry twin HRVs that operate in
a number of viewing configurations and in different spectral modes.
Some of those viewing configurations and spectral modes include one HRV only operating in
a dual spectral mode (i.e., in both panchromatic mode and multispectral mode); two HRVs
operating in the twin-viewing configuration (i.e., one HRV in panchromatic mode and one
HRV in multispectral mode); and two HRVs operating independently of each other (i.e., not
in twin-viewing configuration).
HYDROLOGY
Scientific study of the waters of the Earth, especially with relation to the effects of
precipitation and evaporation upon the occurrence and character of ground water.
HYPERTEXT
The use of links between related words, graphics, or documents that allow the user to jump to
associated topics or definitions when reading menus or help files.
HYPSOGRAPHY
The scientific study of the Earth's topologic configuration above sea level, especially the
measurement and mapping of land elevation.
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Initial content for this Glossary of terms has been graciously supplied by RADARSAT International - www.rsi.ca
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