Related Information Calibration and Optical Research Laboratory Calibration Facilities Calibration Capabilities Related Programs SABER Cassini-Huygens Website Galileo SSI Website Galileo Project Mars Reconnaissance Orbiter

Off-Axis Scatter Measurement

SDL's optical design and testing expertise supports programs where the off-axis rejection performance of sensors is critical to data validity. In addition to providing software stray light analyses, SDL has the capability to make off-axis measurements at ultraviolet, visible, and near-IR wavelengths. An upgrade is in progress that will enable testing at 10.6 microns. Measurements are made in a specially designed, class-100 cleanroom chamber that minimizes the amount of scattered light from the optical system that re-enters the system. This unique facility prevents data corruption and has allowed the off-axis response to be measured nearly 12 orders of magnitude down from the peak on-axis response, demonstrating a very low noise floor (see Figure 1).

Figure 1. Measured Off-Axis Response of the Cassini Narrow Angle Camera

Several system-level off-axis scatter measurements have been made on space sensors in SDL’s facility. Most recently, the off-axis response to a simulated point source was measured for the Mars Reconnaissance Orbiter’s Optical Navigation Camera (ONC). Other space sensors that have been measured include the SABER telescope aboard TIMED, the Cassini Narrow Angle Camera (NAC), and the Galileo Solid State Imaging (SSI) camera.

An off-axis scatter measurement provides a crosscheck with software analysis. Discrepancies between the two can be attributed to optical or mechanical differences between the tested unit and software model, missed stray light paths, "actual versus estimated" scatter characteristics of the optical surfaces, and measurement setup problems. A comparison of the SABER measurement to a software prediction is shown in Figure 2 (below). This chart indicates that the actual scatter properties of the SABER optics are better than those used in the software model. At off-axis angles less than 3 degrees, the measured data has been contaminated by scatter from the point source collimating mirror, which has since been replaced with a low scatter mirror.

Figure 2. Comparison of the Measured and Predicted Off-Axis Response of SABER

References

Andrew E. Lowman, and John L. Stauder, “Stray light lessons learned from the Mars Reconnaissance Orbiter’s Optical Navigation Camera,” Stray Light in Optical Systems: Analysis, Measurement, and Suppression, Proc. SPIE, vol. 5526B, August 2004.

J.L. Stauder, L.R. Bates, R.W. Esplin, J.S. Dyer, and D.O. Miles, “Off-axis response measurement of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) telescope,” Current Developments in Lens Design and Optical Engineering II, Proc. SPIE, vol. 4767, July 2002.

J.C. Kemp, J.L. Stauder, S. Turcotte, and H.O. Ames, “Terrestrial “black hole” for measuring high-rejection off-axis response,” Infrared Spaceborne Remote Sensing V, Proc. SPIE, vol. 3122, pp. 45-56, July 1997.