A necessary condition for accumulating fundamental climate data records is the use of observation instruments whose stability and accuracy are sufficiently high for climate monitoring purposes; the number of instruments and their distribution in space should be sufficient for measurements with no spatial or temporal gaps. The continuous acquirement of data over time intervals of several decades can only be possible under the condition of simultaneous application of instruments produced by different manufacturers and installed on different platforms belonging to one or several countries. The design of standard sources for pre-flight calibrations and in-flight monitoring of instruments has to meet the most stringent requirements for the accuracy of absolute radiometric measurements and stability of all instruments. This means that the radiometric scales should be stable, accurate, and uniform. Current technologies cannot ensure the high requirements for stability and compatibility of radiometric scales: 0.1% per decade within the 0.3 - 3 µm band and 0.01 K per decade within the 3 - 25 µm band. It is suggested that these tasks can be aided through the use of the pure metals or eutectic alloy phase transition phenomenon that always occur under the same temperature. Such devices can be used for pre-flight calibrations and for on-board monitoring of the stability of radiometric instruments. Results of previous studies of blackbody models based upon the phase transition phenomenon are quite promising. A study of the phase transition of some materials in small cells was conducted for future application in onboard monitoring devices and its results are positive and allow us to begin preparations for similar experiments in space.
Previous successful international cooperative efforts offer a wealth of experience in dealing with highly sensitive issues, but cooperative remote sensing for monitoring and understanding the global environmental is in the national interest of all countries. Cooperation between international partners is paramount, particularly with the Russian Federation, due to its technological maturity and strategic political and geographical position in the world. Based on experience gained over a decade of collaborative space research efforts, continued cooperation provides an achievable goal as well as understanding the fabric of our coexistence. Past cooperative space research efforts demonstrate the ability of the US and Russian Federation to develop a framework for cooperation, working together on a complex, state-of-the-art joint satellite program. These efforts consisted of teams of scientists and engineers who overcame numerous cultural, linguistic, engineering approaches and different political environments. Among these major achievements are: (1) field measurement activities with US satellites MSTI and MSX and the Russian RESURS-1 satellite, as well as the joint experimental use of the US FISTA aircraft; (2) successful joint Science, Conceptual and Preliminary Design Reviews; (3) joint publications of scientific research technical papers, (4) Russian investment in development, demonstration and operation of the Monitor-E spacecraft (Yacht satellite bus), (5) successful demonstration of the conversion of the SS-19 into a satellite launch system, and (6) negotiation of contractual and technical assistant agreements. This paper discusses a new generation of science and space capabilities available to the Remote Sensing community. Specific topics include: joint requirements definition process and work allocation for hardware and responsibility for software development; the function, description and status of Russian contributions in providing space component prototypes and test articles; summary of planned experimental measurements and simulations; results of the ROKOT launch system; performance of the Monitor-E spacecraft; prototype joint mission operations control center; and a Handbook for Success in satellite collaborative efforts based upon a decade of lessons learned.
The demands of modern radiation thermometry and radiometry are being satisfied by a large variety of high-precision unique BB sources (both fixed-point and variable temperature) designed for a wide range of temperature from 100 K to 3500 K. The paper contains a detailed review of low-, medium- and high-temperature precision blackbodies developed at VNIIOFI as the basis of the spectral radiance and irradiance calibration devices in the rank of National standards. The blackbodies include: 1) variable-temperature (100K..1000K) research-grade extended-area (up to 100 mm) models intended to perform radiometric calibrations by comparison with a primary standard source, as well as can be used as the sources for high-accuracy IR calibration of space-borne and other systems not requiring a vacuum environment; 2) low-temperature fixed-point blackbodies on the basis of phase transitions of pure metals such as In and Ga sources, and the metal-metal eutectics operating within the medium-temperature range (300K to 400K); these are used for pyrometric measurements, IR-radiometry, preflight and (future aspects) in-flight calibration of space borne IR instruments; 3) high-temperature wide aperture variable-temperature blackbodies (1800K to 3500K) such as BB3500MP, BB3500YY designed and fabricated, along with fixed-point cells working above the ITS-90 temperatures on the basis of phase transitions of metal-carbon eutectic alloys (Re-C, TiC-C, ZrC-C, HfC-C), which possess unique reproducibility of 0.1% or less.
The state-of-the-art electro-optical sensors being designed for today's space-based environmental applications require a complete characterization and thorough calibration. This is especially true for sensors designed to assess global climate change, which require very small uncertainties. This paper describes a system-level approach that addresses each phase of calibration, from planning to on-orbit operations. This approach encourages early planning and continuity of effort throughout the lifetime of the project (pre- and post-flight) to promote an optimum calibration approach that will minimize uncertainty for the intended application. This paper also discusses considerations for component level characterization, ground calibration and standards, in-flight calibration sources and trending, and in-flight validation assessment.
John DeVore, A. Stair, Thomas Humpherys, Valery Sinelshchikov, Ilya Schiller, Victor Misnik, Vladimir Ivanov, Valery Kirichouk, Valery Abramov, John Watson, Dmitry Chvanov, Victor Privalsky
We describe joint U.S.-Russian Federation (RF) measurements of cloud scattering and polarization using the cloud chamber at Obninsk and field observations at Gorno-Altaysk. Cloud chamber experiments measure polarized scattering patterns of narrow distributions of ice crystals. These experiments may be supplemented with extended-range, intensity-only measurements. The U.S. team uses its scattering codes to verify intensity measurements involving oriented ice crystals, compares the orientation distributions with theory, and may field sensors to measure the total optical depth and the forward scattering properties of the particles in the cloud layer. Ice clouds present two serious impediments to electro-optical observation systems: clutter in short and mid-wave IR bands, and propagation loss when attempting to see through clouds. In high-altitude clouds, ice particles' mirror-like crystalline structure can produce intense "glint" features viewed from satellite sensors. Polarization can mitigate cloud clutter, since cloud-scattered sunlight is generally polarized, whereas point-source target signals are not. The effectiveness of polarization as a mitigant can in principle be modeled, but the models require validation, which must be based on carefully designed laboratory and field experiments.
The full potential of current remote sensor technology is limited by the inability to correct biases once an exo-atmospheric remote sensor becomes operational. Even when the calibration is traced to the International System of Units, SI, and the instrument is performing within the operational envelope wherein it is calibrated, the problem exists and a Space Metrology Program is a potential solution to the problem. This paper discusses such a program, suggests a feasibility study to address the issues and recommends a plan of action.
Any operational instrument has a bias and reducing the magnitude of the bias can only be accomplished when an adequately accurate standard is accessible by the instrument while the instrument is in its operational environment. Currently the radiometric flux from the sun, the moon and the stars is inadequately accurate SI to provide a standard that is consistent with the remote sensor state-of-the-art technology. The result is data that is less accurate than it could be often leading to confusing and conflicting conclusions drawn from that data. Planned remote sensors such as those required to meet future program needs (e.g. the United States National Polar-Orbiting Operational Environmental Satellite System (NPOESS) and the proposed international Global Earth Observation Program) are going to need the higher accuracy radiometric standards to maintain their accuracy once they become operational. To resolve the problem, a set of standard radiometers on the International Space Station is suggested against which other exo-atmospheric radiometric instruments can be calibrated. A feasibility study for this program is planned.
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