Diffraction Effects in Remote-Sensing Instruments and SI Traceability

Details Diffraction Effects in Remote-Sensing Instruments and SI Traceability Diffraction Effects in Remote-Sensing Instruments and SI Traceability

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmgc23a0762s&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #GC23A-0762

Computer Science

Sound

0669 Scattering And Diffraction, 0689 Wave Propagation (2487, 3285, 4275, 4455, 6934), 1640 Remote Sensing (1855), 1650 Solar Variability (7537), 1694 Instruments And Techniques

Scientific paper

Relevant climate-related measurements from space demand high accuracy and SI traceability, which allows different measurements to be compared to each other even when they are made decades apart. Irradiance or spectral irradiance at an instrument's sensor pupil corresponds to other quantities of interest, such as the earth's solar reflectance. However, understanding an instrument's geometrical throughput with sufficient accuracy may not be enough to characterize the optical system between entrance pupil and detector. In fact, geometrical optics is only an approximate description of the propagation of light. One critical example of the difficulties lies in the measurement of total solar irradiance (TSI), where diffraction has a relative effect on the apparent solar irradiance by over 1600 ppm when comparing different radiometers. In addition, determining the spectral irradiance of stellar calibration sources requires the understanding of diffraction effects in sensor optics as well as laboratory optics used to calibration such sensors. In all of the above cases, losses or gains in flux can arise because of diffraction. More subtle, though, is the role played by mutual coherence effects. As compared to ray propagation, mutual coherence of light propagates through an optical system and is the observable quantity of interest. This implies that the diffraction effects arising at different stages in the optics cannot be calculated separately and then directly combined. Instead, one must consider the wave propagation of light through one's entire optical system. This can arise for subtle reasons, including having apertures or baffles that are nearly vignetting each other. In addition, in the Atmospheric Infrared Sounder (AIRS) instrument's optical train, the imaging optics that focus light onto a spectrometer entrance slit present the light as a coherent wave over the entire slit for each primary source point. The primary source is spatially incoherent. Averaging over all source points, the field is partially coherent at the entrance slit. Consequently, the slit itself cannot be treated as an incoherent source when determining the spectral transmission function and throughput of the spectrometer.

Affiliated with

Also associated with

No associations

Rating

Diffraction Effects in Remote-Sensing Instruments and SI Traceability does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Diffraction Effects in Remote-Sensing Instruments and SI Traceability, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Diffraction Effects in Remote-Sensing Instruments and SI Traceability will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1242041