An application-specific contracted integrating sphere source of uniform spectral radiance is described. The source is used for pre-launch test and calibration of imaging radiometers which will be used as satellite borne earth remote sensors. The calibration source is primarily intended to serve as a transfer standard of radiance.Design criteria for the uniform radiance source are presented. Included is a summary of the end-user specifications in regards to spectral radiance, radiance levels of attenuation, radiance stability, and aperture uniformity. Radiometric theory used to predict the source radiance for a specific spectral flux input is reviewed. Reasoning for the use of an integrating sphere platform for this application and characteristic features of the source are discussed.Calibration methods and instrumentation are described. The resultant data presented include the modeled data compared with the measured performance. Methods of data reduction and uncertainty are addressed where applicable.

Sintered polytetrafluoroethylene (PTFE) is an extremely stable, near-perfect Lambertian reflecting diffuser and calibration standard material that has been used by national labs, space, aerospace and commercial sectors for over two decades. New uncertainty targets of 2 % on-orbit absolute validation in the Earth Observing Systems community have challenged the industry to improve is characterization and knowledge of almost every aspect of radiometric performance (space and ground). Assuming “near perfect” reflectance for angular dependent measurements is no longer going to suffice for many program needs. The total hemispherical spectral reflectance provides a good mark of general performance; but, without the angular characterization of bidirectional reflectance distribution function (BRDF) measurements, critical data is missing from many applications and uncertainty budgets. Therefore, traceable BRDF measurement capability is needed to characterize sintered PTFE’s angular response and provide a full uncertainty profile to users. This paper presents preliminary comparison measurements of the BRDF of sintered PTFE from several laboratories to better quantify the BRDF of sintered PTFE, assess the BRDF measurement comparability between laboratories, and improve estimates of measurement uncertainties under laboratory conditions.

Integrating spheres for optical calibration of remote sensing cameras have traditionally been made with Quartz Tungsten Halogen (QTH) lamps because of their stability. However, QTH lamps have the spectrum of a blackbody at approximately 3000K, while remote sensing cameras are designed to view a sun-illuminated scene. This presents a severe significant mismatch in the blue end of the spectrum. Attempts to compensate for this spectral mismatch have primarily used Xenon lamps to augment the QTH lamps. However, Xenon lamps suffer from temporal instability that is not desirable in many applications. This paper investigates the possibility of using RF-excited plasma lamps to augment QTH lamps. These plasma lamps have a somewhat smoother spectrum than Xenon. Like Xenon, they have more fluctuation than QTH lamps, but the fluctuations are slower and may be able to be tracked in an actual OGSE light source. The paper presents measurements of spectra and stability. The spectrum is measured from 320 nm to 2500 nm and the temporal stability from DC to 10 MHz. The RF-excited plasma lamps are quite small, less than 10mm in diameter and about 15 mm in length. This makes them suitable for designing reasonably sized reflective optics for directing their light into a small port on an integrating sphere. The concludes with a roadmap for further testing.

Application-specific integrating sphere-based, integral veiling glare measurement systems are described. The sources use the integral method for measuring the veiling glare (VG) index of various lens-based imaging systems. The calibration source has provisions in the form of a collimating lens holder to simulate a situation where the black target and bright surround are at a sufficiently great distance to give measurements of VG index which are the same as that which would result if the distance where infinite. The design criteria for the integral VG test source are presented. Included is a summary of the end-user specifications in regards to spectral radiance, levels of attenuation, irradiance stability, and aperture uniformity and contrast. Spectral radiometric predictions and actual output levels are compared Veiling Glare (VG) is completely defined in ISO-9358, but for expediency, it will be defined in this section with reference to Figure 1 for clarity. The illuminance of the focal plane is scanned while the lens system being evaluated views a uniform hemispherical radiance field created by an integrating sphere. The lens system also images a black spot (light trap with negligible reflectance) while scanning the focal plane field. The ratio of the illuminance at the focal plane of the lens while looking at the light trap to the illuminance of the sphere wall with no trap is the VG index. This ratio must also account for the ratio of the reflectance of the light trap to the reflectance of the sphere wall.AM1 is the spectral irradiance at the surface of the earth with the sun positioned directly overhead; i.e., light from the sun must travel through 1 air mass before reaching the ground. INTRODUCTIONThere are two systems described for measuring VG of a device under test (DUT). The two systems represent the extreme range of applications for the systems developed by Labsphere. The first system measures the VG for a groundbased, low light level night vision system which requires a CCT of 2856K and a luminance level in the range of 5 to 5E-5 foot-Lambert (fL). The second system required luminance levels above AM1 from 400-900 nm and provided radiance (no specification) from 250-1100 nm. In this case, AM1 was presented as spectral irradiance in units of W/m2-u.

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