The CrIS (Cross-track Infrared Sounder) instrument collects IR spectral radiance data to calculate calibrated atmospheric temperature, pressure, and moisture profiles for the NPOESS (National Polar-orbiting Operational Environmental Satellite System) program. CrIS features a Michelson Interferometer with three spectral bands (SWIR to LWIR), each with a 3 by 3 array of circular sensing apertures at the focal plane. The optical design includes a folded Gregorian telescope after the interferometer, a field stop to define the sensing aperture array, and collecting optics to place the interferogram energy onto the photovoltaic HgCd detectors. Many trade studies and analyses were performed to determine the design of the optical system, including telescope configuration, pupil locations, elimination of channelled spectra, polarization sensitivity, stray energy rejection, and compact packaging. This paper will describe the trade studies and analysis performed during the design of the CrIS instrument optics.
One of the sub-tasks for the GOES N/O program is to redesign the assembly/test program to reduce instrument test time and to make test results more comparable to data that can be taken on orbit and at the spacecraft integrator's facility. Currently, ITT A/CD measures the instrument MTF at specific spatial frequencies using a collimator and bar targets. This gives only a few individual points on the MTF curve. To improve this production test, the MTF will now be measured by scanning a single slit target. The result of this slit scan is the Line Spread Function (LSF) and the Fourier Transform of the LSF yields the continuous frequency MTF curve. Obtaining this curve with a single target eliminates the need for repeated scans using different spatial frequency targets. A problem with scanning a slit for this application is the number of samples taken across it is very few when the GOES scanner is running at operational speed. Two methods to collect multiple scan lines and recombining the scans to get a `highly sampled' scan of the slit have been considered. This paper discusses the two approaches and presents a validation of the slit scan method for both a slow scan of the target and for an operational speed scan where multiple scan lines are recombined to give a highly sampled slit.
One of the primary difficulties with high altitude airdrop missions is the effect of the wind field on the objects dropped. Aircraft crews currently obtain wind fields using a combination of measuring winds at altitude during flight, data from local weather stations and data from balloon launches (radiosondes). This data is used to adjust the cargo release point to compensate for the intervening winds. Since these methods have limited utility, a desired alternative would be a sensor placed on board the aircraft able to accurately measure real time wind fields at any location. The purpose of the project presented is to demonstrate a flightworthy eye-safe solid state laser radar system meeting these criteria. The system, which was assembled from available subsystems not designed nor engineered for this particular application, was named `Interim Operational Capability'. These subsystems were hardened and integrated together in such a way as to be installed on an operational Air Force aircraft in a short time-frame, thereby providing a near term wind field measuring capability for airdrop missions, should the need arise.
A 2.09-μm ladar system is built to compare coherent to incoherent detection. The 2.09-μm wavelength is of interest because of its high atmospheric transmission and because it is eyesafe. The 2.09-μm system presented is capable of either a coherent or incoherent operational mode, is tunable in a small region around 2.09 μm, and is being used to look at the statistical nature of the ladar return pulses for typical glint and speckle targets. To compare coherent to incoherent detection the probability of detection is investigated as the primary performance criterion of interest. The probability of detection is dependent on both the probability of false alarm and the probability density function, representing the signal current output from the detector. These probability distributions are different for each detection technique and for each type of target. Furthermore, the probability of detection and the probability of false alarm are both functions of the dominating noise source(s) in the system. A description of the theoretical expectations of this system along with the setup of the ladar system and how it is being used to collect data for both coherent and incoherent detection is presented.