- Industry: Aerospace
- Number of terms: 16933
- Number of blossaries: 2
- Company Profile:
The Executive Branch agency of the United States government, responsible for the nation's civilian space program and aeronautics and aerospace research.
The empirical calibration of satellite sensors by measurement of upwelling radiation from targets that are viewed on the ground or from aircraft at the same time as from space. The at-satellite radiance is calculated by using radiative transfer models of the atmosphere along with measurements of the atmospheric transmittance or optical thickness for the spectral band-pass being calibrated. Also see ground truth/ground observations, radiometric reflective band calibration, and reflectance-based calibration.
Industry:Aerospace
The extent of lateral overlap between images acquired over adjacent ground tracks. Sidelap increases with distance from the equator.
Industry:Aerospace
The field calibration of satellite sensors by measurement of reflected solar radiation from targets of known or measured reflectance that are viewed on the ground at the same time as from space. The at-satellite radiance is calculated by using radiative transfer models of the atmosphere along with measurements of the atmospheric transmittance or optical thickness for the spectral band-pass being calibrated. Also see ground truth/ground observations, radiance-based calibration, and radiometric reflective band calibration.
Industry:Aerospace
The geometric description of a detector’s instantaneous field-of-view (IFOV) from the satellite. The modulation transfer function (MTF) is a frequency-based characterization of the IFOV of the plane area of a specific detector that is both sensitive to and exposed to radiation from the imaging optics. The full-width-at-half-maximum (FWHM) of a 2-dimenstional line-spread function is a spatial representation of IFOV. MTF is the ratio of the contrast of the output to the input image as a function of frequency. MTF is defined as the magnitude of the Fourier transform of the line spread function. Common units of IFOV are radians, steradians (sr) or degrees. Because of the common optics and the similar size, detectors within a spectral band are usually assumed to have identical IFOVs. An IFOV expressed in spatial rather than angular units, such as 30 m for a TM detector, is altitude-dependent. An instrumental in-vacuum MTF is modulated further by the atmosphere, which broadens the nominal instrumental IFOV, such that it is not possible to resolve features as easily on the ground. If the structural aspects of the optics of the imager are changing with time from factors such as expansion or contraction from outgassing of water in space, then the IFOV or MTF will also change. Also see geometric image calibration and point spread function.
Industry:Aerospace
The ground trace of a narrow strip that is recorded by the instantaneous field of view of a detector in a scanner system.
Industry:Aerospace
The inferring of spatial characteristics of the instrument from the collected image of a point source such as a star. Also see modulation transfer function.
Industry:Aerospace
The interval in time between successive passages (orbits) of a satellite through a reference plane. The orbital period of Landsat 7 is about 1.5 hours.
Industry:Aerospace
The latitudinal (nominal) centerline of a Landsat scene. Row 60 corresponds to lat. 0° (the equator), row 1 is at lat. 80°47' N, and row 122 is at lat. 81°51' S. There are 248 rows, altogether, for Landsat 4, 5, and 7, the same as for the earlier Landsats 1,2, and 3.
Industry:Aerospace
The location of every pixel in a 2-dimensional satellite image to a specific spatial location on the ground. Geometric calibration may be done by either re-sampling the image in a specific projection or by storing the geometric location information with each pixel in the image. If pre-launch values of the instrument “MTF” have been accurately enough made prior to launch, then an MTF correction can also be made as part of the geometric ground processing. Resampling for TM-type imagery is usually done using cubic convolution algorithms with an accuracy of ±50 m for 30 m ETM+ pixels from inputs that include “definitive” ephemeris and known characteristics of the non-uniform scan rate. This geodetic accuracy refers to how close the knowledge of the pixel’s location is to the actual location on the Earth. MODIS sensors on the Terra and Aqua satellites store calibrated imagery as geolocated information for each pixel. Systematic geometric corrections correct for sensor-related factors, either with or without the use of ground control points for the specific image. Such systematic products can be significantly improved if topographic information is available and used. In TM-era products the approximate 8-bit radiometric precision was reduced with each geometric re-sampling, often by simple rotation and translation, to a new 8-bit product, and therefore it was desirable when radiometrically or geometrically re-calibrating an image, to normalize it to best estimates, to start from raw uncalibrated imagery. Also see modulation transfer function and scan line length.
Industry:Aerospace
The longitudinal center line of a Landsat scene corresponding to the center of an orbital track. Sequential numbers from east to west are assigned to 233 nominal satellite tracks for Landsat 4, 5, and 7. Path numbers can be used with row numbers to designate nominal scene center points. See row and scene center, nominal.
Industry:Aerospace
