What is radiance in remote sensing?
Radiance is directly measured by remote sensing instruments. Radiance includes the radiation reflected from the surface, in addition to the radiation that bounces in from neighboring pixels, and the radiation reflected from clouds.
What is path radiance?
Path radiance is the radiance detected by a spaceborne sensor above a nonreflective surface and is the result of backscattering to space by particles and molecules in the atmosphere. In specific measurement conditions the path radiance can be measured also from the ground.
What causes path radiance?
At longer wavelengths, the thermal emissions of the object and of the atmosphere give rise to the image and atmospheric background (path radiance) irradiances, respectively, since at such longer wavelengths they are of greater irradiance than sunlight.
What is bottom atmosphere?
The Bottom Of Atmosphere (BOA) reflectance, also known as the surface reflectance, i.e., satellite derived Top Of Atmosphere (TOA) reflectance corrected for the scattering and absorbing effects of atmospheric gases and aerosols, is widely used to monitor the land surface reliably and generate the greater majority of …
How does path radiance affect remote sensing?
First, it modifies the spectral and spatial distribution of the radiation incident on the surface. Second, radiance being reflected is attenuated. Third, atmospheric scattered radiance, called path radiance, is added to the transmitted radiance.
What is the total radiance measured at the sensor?
Radiance at the Sensor’s Aperture Radiance is the “flux of energy (primarily irradiant or incident energy) per solid angle leaving a unit surface area in a given direction”, “Radiance is what is measured at the sensor and is somewhat dependent on reflectance” (NASA, 2011, p. 47).
What is atmospheric correction of satellite imagery?
Atmospheric correction is the process of removing the effects of the atmosphere on the reflectance values of images taken by satellite or airborne sensors. Atmospheric effects in optical remote sensing are significant and complex, dramatically altering the spectral nature of the radiation reaching the remote sensor.
What does TOA radiance correct for?
First, it removes the cosine effect of different solar zenith angles due to the time difference between data acquisitions. Second, TOA reflectance compensates for different values of the solar irradiance arising from spectral band differences.
How is the reflectance spec-Trum used in remote sensing?
Since the reflectance spectrum is independent of the illumination, the reflectance spec- trum provides the best opportunity to identify the materials in a scene by matching the scene reflectance spectra to a library of known spectra.
Which is the correct definition of irradiance and radiance?
•Irradiance: The amount of energy incident on a given area of a surface in a given amount of time (W/m2). •Radiance: The amount of energy scattered in a particular direction (W/m2/sr). •Solid angle: The ratio of the area of a spherical surface to the square of the radius. Ω = A/r2 Ω Basic Radiometric Terms A r
How are units of Radiance used in spectral imaging?
Normaliz- ing the radiance by the wavelength of the light, which is typically specified in microns (µm), yields spectral radiance, with units of W/m2/µm/steradian. Reflectance Spectrum We are accustomed to using color as one of the ways we distinguish and identify materials and objects.
What is hemispherical transmittance and absorptance in remote sensing?
•Hemispherical transmittance: The ratio of the radiant flux transmitted through a surface to the radiant flux incident to it. •Hemispherical absorptance: The ratio of the radiant flux absorbed by a surface to the radiant flux incident to it.