ABSTRACT: Landsat sensors have been in operation since 1972 beginning with the Return Beam Videocon (RBV) on L1-3, the Multi Spectral Sensor (MSS) on L1-5, the Thematic Mapper (TM) on L4-5, and the Enhanced Thematic Mapper (ETM+) on L7. During the accumulated 36 year operational period many calibration scenarios have existed under the control of government and private entities which taken together complicate the history of the Landsat project and raise questions about the technical quality of early datasets residing in the national archive. Given the importance of this historical data in land and climate change studies, effort must be given to assuring all datasets are calibrated in a consistent, clearly understood, manner before dissemination to the research community.

Beginning with the launch of L7-ETM+ an Image Assessment System (IAS) has been in place at the NASA Landsat Project Science Office and the EROS Data Center to enable image processing, calibration data analysis, and assist with creation of Calibration Parameter Files (CPF’s) used to drive the production system providing data to the Landsat user community. The IAS is designed to assure a mechanism exists to both analyze data and maintain critical results for the long term.

Development efforts are currently underway to extend the existing IAS and provide the capability to process and analyze TM and MSS Datasets from 1972 onward. This presentation will brief the goals, objectives, current status, algorithms, and technical details of the radiometric components of the extended system. Challenges of handling data ranging in time scales ranging from ms-to-decades will be discussed, along with a quick look at some early trending results from the L5-TM instrument (now operational for over 24 years) based on a sampling of the national data archive. Status and challenges of L4-TM and L1-5 MSS activities will also be presented as time allows.

MIC5 Calibrator Fabrication and Characterization: Alan Bird, Joseph Tansock, Alan Thurgood, Scott Hansen – USU/Space Dynamics Laboratory; Dave Perkes – ATK Mission Research Corporation; Deon Dixon, Steven Brown, Karl Burk, Mark Greenman, James Peterson, David Marchant, Dean Ferguson, Brent Haslem – USU/Space Dynamics Laboratory

ABSTRACT: The Multifunction Infrared Calibrator, MIC5, is the latest calibration chamber acquired by the Space Dynamics Laboratory (SDL). The chamber and optics were fabricated by ATK Mission Systems. MIC5 can be operated at ambient or cryogenic temperatures. Cryogenic testing has been performed at liquid nitrogen temperature, although the system is designed to operate at liquid helium temperature. MIC5 incorporates a 16 inch collimator that includes a remotely controlled pointing mirror and remotely controlled aperture and filter wheels. A remotely controlled 3-axis translation stage provides the ability to position the apertures relative to the focus of the collimator. SDL-fabricated full-aperture and Jones sources provide input for small-signal linearity measurements. Thermal and mechanical systems are computer controlled with a user-friendly graphical interface that also provides for automated (scripted) operation. The MIC5 system includes an automated data collection system that can also provide communication to the unit under test. Together, the automated hardware and data collection systems provide an efficient means to collect complex calibration datasets. The MIC5 system was characterized at SDL from January to March, 2008. This presentation describes the MIC5 calibrator and provides a detailed summary of its characterization.

Performance of the Cryogenic Michelson Interferometer: Philippe Lagueux, André Villemaire, Martin Chamberland – Telops Inc; Adriaan Carter – NIST

ABSTRACT: A cryogenic Fourier transform infrared spectrometer (Cryo-FTS) was developed for the Low Background Infrared (LBIR) facility at the National Institute of Standards and Technology (NIST). This spectrometer was developed for the Missile Defense Agency Transfer Radiometer (MDXR) that will be used to calibrate infrared sources that can not be transported to NIST for calibration.

The Cryo-FTS spectral range is nominal from 4 to 15 μm and a spectral resolution of 0.6 cm-1. The compact Michelson interferometer has an operating temperature range between 10 K and 340 K with very low static beam redirection. It integrates a digitally servo-controlled porchswing mechanism to provide an accurate and repeatable optical path difference and is supported by a Wavefront Alignment (WA) system to correct for wavefront residual tilt in real time using a fibre optic based metrology system.

The Cryo-FTS was integrated and tested for modulation efficiency, static and dynamic beam redirection, relative spectral amplitude. The preliminary performance testing results are presented in this paper.

Novel Cryogen–Free Calibration Sources in the Infrared: Tanya Myers, Bret Cannon, Bryan Broocks – Pacific Northwest National Laboratory

ABSTRACT: Passive infrared sensor data must be converted from raw digital counts to accurately calibrated physical measurements for meaningful data. Accurate conversion is challenging but necessary to compare responses of different sensors, to monitor changes through time, and to provide users with physical data that do not depend on the sensor. A thorough calibration can introduce time delays so that methods for rapid calibration are desirable. Although an extensive pre-mission calibration is usually performed, an on-board calibration is vital to monitor sensor temporal changes. Conventional blackbodies are usually selected for this application but impose serious weight and power burdens on the sensor system payload and offer only a single radiometric level to each sensor passband.

Quantum cascade lasers (QCLs) are semiconductor devices that can now operate at room temperature avoiding the requirement for cryogenic cooling. These novel room temperature devices provide an alternative technology for calibration sources in the infrared due to their radiometric and spectral stability and repeatability. QCLs are lightweight and can rapidly reach stable output levels upon turn-on from a cold start so that they only draw power when needed and can be quickly switched from one radiometric level to another to cover the sensor’s dynamic range. Since the output power can be adjusted rapidly to span the dynamic range of the detector, QCLs can provide a nonlinearity correction on a fast timescale by increasing the number of radiance levels used in the radiometric calibration. Thus, QC lasers can provide a useful complement to blackbodies to improve the overall characterization and calibration of infrared instruments while minimizing the impact on instrument size, weight, and power. This paper describes a measurement sequence that provides multiple radiometric levels in under 100 seconds with better than 1% repeatability for more than 300,000 cycles or more than 8300 hours of operation.

Diffraction Analysis in Optical Design: Eric Shirley, Adriaan Carter – NIST

ABSTRACT: Optical design is usually based on geometrical optics and conventional radiometric definitions. Some features of optical layouts, such as Lyot stops and other field stops, may be included in optical systems to minimize stray light and/or effects of aberrations. Because of diffraction, these and all other optical elements can undermine the basic formulas for throughput of optical systems based on geometrical optics. Furthermore, the related difficulties are more severe at longer wavelengths. Thus, experience gained in visible optics might not ensure adequate appreciation of effects that are more severe in the infrared region.

In this presentation, we intend to highlight the main effects of diffraction and ways to minimize them. Accounting for any remaining diffraction effects in the form of diffraction corrections relies on calculations. Ways to ensure the possibility of obtaining straightforward, meaningful corrections will also be discussed. Conversely, practices that should be avoided, which complicate diffractions effects, will also be discussed.

Capability of Low Reflectance Measurements by an Infrared Laser–based Reflectometer: Jinan Zeng, Leonard Hanssen – NIST

ABSTRACT: An instrument, the Complete Hemispherical Infrared Laser-based Reflectometer (CHILR), has been designed and built for the accurate characterization of the total reflectance of highly absorbing samples and cavity structures down to the 10-5 level. The design of CHILR employs a number of the same features of Total Integrated Scatter (TIS) measurement devices, but is used for total reflectance (both specular and diffuse components), rather than only the diffuse component. A number of features of CHILR include spatial uniformity and angular dependence of reflectance measurement capability, multiple wavelength laser sources, and the ability to measure a wide range of sample sizes and cavities with aperture sizes, ranging from 6 mm to 100 mm. We will address several basic issues of alignment, background and externally scattered light, reference measurement, and laser drift, for the CHILR. We will present results of several examples, including cavities for blackbody sources, radiometer cavities for solar irradiance measurement, and a domed coated pyroelectric detector.

Concept for a Space–Based Transfer Standard Spectroradiometer: Don Heath – Ball Aerospace & Technologies Corporation

ABSTRACT: A concept for a space-based transfer standard spectroradiometer that provides a direct transfer of spectral irradiance of the solar disc to measurements of spectral irradiance of the Earth’s disc (or the lunar disc) from GEO and LEO orbits is presented. A simple geometrically baffled instrument is calibrated against NIST radiometric standards on the ground for spectral radiance or irradiance measurements. The instrument consists of multiple detectors, utilizing radiometrically stable ion-assisted-deposition or ion-beam-sputtered narrow band interference filters. The detectors for the solar reflective region are un-cooled Si photodiodes and thermoelectrically cooled InGaAs photodiodes High sensitivity un-cooled thermopiles are used in the thermal infrared. An orthogonal 2-mirror system cancels the polarization effects and is used to view the Sun, Earth, Moon, or space from GEO or LEO orbits. From LEO orbits the instrument views horizon to horizon swaths of the Earth. The swath width is determined by the altitude of the LEO orbit and the geometrical F-number of the system of detector-filter combinations.

During the daylight side of the orbit the solar irradiance is measured at least once, and lunar observations are restricted to the night side of the orbit. The proposed instrument has a wavelength range from about 300 nm to beyond 15 μm. Lunar irradiance measurements are restricted to the solar reflective wavelength region with a long wavelength limit of about 2.4 μm. Currently, work is in progress to define an instrument that is simple in design, low in cost, compact, light weight, and capable of making accurate ratio measurements that are invariant with time over the temporal measurement intervals. The concept instrument would provide albedo measurements in the solar reflective region and thermal emission measurements of the Earth and its atmosphere relative to the irradiance of the Sun. The latter is possible due to the dilution of solar radiance by the solid angle of the Sun. The basic underlying assumption of the concept of a space-based transfer standard spectroradiometer is that the Sun is the most stable radiometric calibration source in space for the wavelength region from 300 nm to beyond 15 μm. Ratio measurements have a potential for very high accuracy over moderately short intervals of time, minimizing instrument degradation effects significantly.