- 업종: 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 process by which electromagnetic energy is propagated through free space by virtue of joint undulatory variations in the electric and magnetic fields in space. This concept is to be distinguished from conduction and convection. Also, the process by which energy is propagated through any medium by virtue of the wave motion of that medium, as in the propagation of sound waves through the atmosphere. Also called radiant energy and electromagnetic radiation.
Industry:Aerospace
The process by which electromagnetic radiation (EMR) is assimilated and converted into other forms of energy, primarily heat. Absorption takes place only on the EMR that enters a medium, and not on EMR incident on the medium but reflected at its surface. A substance that absorbs EMR may also be a medium of refraction, diffraction, or scattering; however, these processes involve no energy retention or transformation and are distinct from absorption.
Industry:Aerospace
The process of altering the appearance of an image so that the interpreter can extract more information. Some types of digital enhancements commonly applied to Landsat imagery include edge enhancement, noise reduction (filtering), haze removal, and contrast stretching.
Industry:Aerospace
The products of image-forming instruments (analogous to photography). Used loosely, but acceptably, to refer to Landsat image data products.
Industry:Aerospace
The quantitative measurement of the properties of an object at one or several wavelength intervals. Spectral signature analysis techniques use the variation in the spectral reflectance or emittance of objects as a method of identifying the objects, e.g. mineral detection.
Industry:Aerospace
The radiometric response of an electronic detector that converts photons into voltage or current. Detector responsivity includes the end-to-end optical and electrical path, since radiometric calibration involves converting the digital signal into scientific units such as at-satellite radiance. Typically before launch, detectors within each spectral band of an imaging sensor are exposed to full aperture illumination from a uniform source such as a large integrating sphere, which itself has been calibrated against standards that are traceable to National Institute of Standards and Technology (NIST) standards. Absolute detector responsivity is in units of digital number per radiance unit (such as watts per square meter per steradian), or in units of digital number per spectral radiance unit (such as watts per square meter per steradian per micron). Once on-orbit, the detector responsivity is often monitored for possible change with time. Relative gain of the detector in comparison to a reference detector or to an average of detectors within a band can be made from image data by histogram equalization. Absolute gain can be monitored using internal lamps, or external sources such as the Sun, Moon or nearly homogeneous areas on Earth after correcting for atmospheric effects. Also see calibration lamps, NIST traceability, radiometric emissive band calibration, and radiometric reflective band calibration. .
Industry:Aerospace
The radiometrical comparison of one sensor to another sensor on different satellites. Imagers are often considered to be cross-calibrated if they are calibrated to a common source such as an integrating sphere before launch. However, testing for changes with time requires on-orbit cross-calibration being performed by looking at the same target at as close to the same time as possible to avoid possible changes in the target scene, especially atmospheric changes. The best target for this is the Moon because it has no atmosphere and is spectrally flat. The common assumption in cross-calibrations is that the spectral band-passes of the two sensors are identical or that there are no spectral features in the target, including the atmosphere. Even with sensors designed to have nearly identical band-passes, differences in relative spectral response (RSR) curves can result in uncorrectable radiometric differences of 5-15% due to real spectral differences in the target viewed by the two sensors. Also see relative spectral response and spectral striping.
Industry:Aerospace
The range of grey shades from maximum to minimum is divided into contiguous intervals, each of equal length, and each grey shade is assigned to the quantized class which corresponds to the interval within which it lies.
Industry:Aerospace
The ratio of the energy per unit time per unit area (radiant power density) transmitted through an object to the energy per unit time per unit area incident on the object. In general, transmittance is a function of the incident angle of the energy, viewing angle of the sensor, spectral wavelength and bandwidth, and the nature of the object.
Industry:Aerospace
The ratio of the level of the information-bearing signal power to the level of the noise power. SNR determines the precision of a radiometric measurement. The signal-to-noise ratio (SNR) is defined as the value of a measurement over the standard deviation of the measurement and is therefore a unitless variable. Typically, sets of visible reflective bands or sets of emissive bands on a scanner are designed to have approximately equal SNRs, with exceptions being made for poorer SNR in a panchromatic sharpening band as a cost of the higher spatial resolution. SNR is often taken as a time average over both random and systemic variations, however it can be a measure of either total or random noise only. SNR usually increases with increasing signal. Also see noise.
Industry:Aerospace
