This work focuses on the development of a cryogenic optical profilometry system for the measurement of material properties of thin films across a wide temperature range. A cryostat was machined and integrated with a Zygo NewView 600K optical profilometer and vacuum system. Curvature data were taken for a SiN<sub>x</sub> thin film on a GaAs substrate from 300 K down to 80 K. From the curvature data, the coefficient of thermal expansion was calculated. The cryogenic optical profilometry system was benchmarked with a three beam curvature technique, and demonstrated excellent agreement across the full temperature range from 300 K to 80 K
Future improvements in spectral imaging systems can be attained through the integration of MEMS-based optical transmission devices matched with pixelated arrays. Such integrated module designs will require a detailed knowledge of the MEMS device optical properties at high spatial resolution and over a wide range of operating conditions. A substantially automated low-cost optical characterization system has been developed, which enables the optical transmission of the MEMS device be measured with high spatial and spectral precision. This Optical Metrology System (OMS) can focus light on the device under test (DUT) to a spot diameter of less than 30 μm, and characterize devices at near infrared for wavelengths within the spectral band from 1.4 μm to 2.6 μm. A future upgrade to the OMS will enable measurements to be carried out across a wide range of DUT temperatures and with a spectral range from visible to long wave infrared wavelengths.
A number of organizations are using the data collected by the HYperspectral Digital Imagery Collection Experiment (HYDICE) airborne sensor to demonstrate the utility of hyperspectral imagery (HSI) for a variety of applications. The interpretation and extrapolation of these results can be influenced by the nature and magnitude of any artifacts introduced by the HYDICE sensor. A short study was undertaken which first reviewed the literature for discussions of the sensor's noise characteristics and then extended those results with additional analyses of HYDICE data. These investigations used unprocessed image data from the onboard Flight Calibration Unit (FCU) lamp and ground scenes taken at three different sensor altitudes and sample integration times. Empirical estimates of the sensor signal-to-noise ratio (SNR) were compared to predictions from a radiometric performance model. The spectral band-to-band correlation structure of the sensor noise was studied. Using an end-to-end system performance model, the impact of various noise sources on subpixel detection was analyzed. The results show that, although a number of sensor artifacts exist, they have little impact on the interpretations of HSI utility derived from analyses of HYDICE data.
The HYDICE instrument began flying at the beginning of 1995. Since then a large body of data has been acquired--on the ground, from characterization flights and from operational missions. In combination with laboratory data, this has been used to conduct an evaluation of the full system. Overall, performance has matched design predictions quite closely, both with respect to technical specifications and operational characteristics. Some anomalies have been identified. Their causes, the impact they have on data quality and methods of correcting them have been assessed. This paper reports on these findings, provides an updated status of the system, and identifies possible hardware upgrades.
The in-flight radiometric stability of images formed in a single spectral band of HYDICE has been examined under various conditions. In the first, the stability of the combined response of the on-board calibrator and HYDICE was checked by comparing repeated image acquisitions over small targets, a few pixels in size, and then over a uniform, extended target. For the second condition, a new flat-field calibration of the focal plane was used which improved the radiometric stability. It is shown from these results that radiometric stability and accuracy are closely related to target contrast and size. This has important consequences for the empirical line approach to calibration or reflectance retrieval. The third condition included a pitch in the attitude of the aircraft that introduced a marked banding of the image in the vicinity of the 1.38-micrometers band, which is very sensitive to the presence of cirrus-cloud ice crystals. This is believed to be another form of the `spectral jitter' described in other papers in these Proceedings.
The sensor MTF is not only an important descriptor of image quality, but also determines the potential for spatial mixing of spectral signatures in hyperspectral systems. The HYDICE total system MTF has been measured from flight imagery of targets of opportunity, including the Mackinaw Straits Bridge in Michigan and the Chesapeake Bay Bridge at Annapolis, Maryland. The procedures used to derive the MTF are described, and the results are compared to pre-flight laboratory measurements made at Hughes-Danbury Optical Systems. The inflight MTF measurements at 0.5 cycles/pixel are in the range 0.5 to 0.65 in-track, and 0.4 cross-track, which are consistent with the pre-flight measurements.
This paper presents an overview of the HYDICE hyperspectral system, sponsored by the Naval Research Laboratory, built by Hughes Danbury Optical Systems and flown by the Environmental Research Institute of Michigan. HYDICE stands for the Hyperspectral Digital Imagery Collection Experiment. The sensor component of this experiment was procured as a dual use initiative. This unique sensor has pushbroom imaging optics with a prism spectrometer and InSb focal plane array detector. It represents a significant advance in signal- to-noise ratio, spatial and spectral resolution, and radiometric accuracy. This paper describes the system that has been built and flight tested. Differences between the original design and the actual hardware are indicated. The integration of the sensor with the aircraft is explained, including an overview of other on-board capabilities. The way in which the sensor system can be operated is illustrated. Flight test data are currently being analyzed, but selected laboratory performance tests are shown. The overall system flight performance is assessed qualitatively, with reference to laboratory data.
HYDICE (the Hyperspectral Digital Imagery Collection Experiment) is a program to build and operate an advanced airborne imaging spectrometer. Scheduled to be operating in 1994, it will provide high quality hyperspectral data for use by a number of US civil agencies in determining its utility for a wide range of applications, as well as in support of basic research. The current status of the system under construction and plans for its operation are reviewed.