Ocean remote sensing satellites have the advantages of long-distance, non-contact observation with large field of view, all-day, all-weather and real-time imaging, and have become an important means of global marine environment monitoring. The development of marine remote sensing in my country is going through a leap from "following" - "running side by side" - "leading". Quantitative application is the characteristic of marine satellite data application. In order to obtain the corresponding relationship between the input radiation and output of the remote sensing camera, and use it for quantitative inversion of the radiation information of the remote sensing target, the radiation calibration of the remote sensing camera is required. In this paper, starting from the high quantitative calibration index requirements of the new generation of ocean water color and water temperature scanner payload, a set of on-board radiation calibration device is designed and developed to realize the full spectrum, full aperture and full optical path high-precision calibration of the payload. The accuracy of the on-board radiation calibration device: the black body emissivity is 0.98, the measurement and temperature control accuracy is better than 0.05K, the temperature stability is better than 0.05K/30min, and the temperature uniformity is better than 0.2K.
KEYWORDS: Black bodies, Body temperature, Calibration, Temperature metrology, Resistance, Control systems, Satellites, Platinum, Infrared radiation, Cameras
This article elaborates on the working principle of the on-board blackbody calibration system, through the high-performance design and accurate index accuracy of the key indicators of high and low large-aperture surface blackbody (effective emission surface normal emissivity, temperature stability, temperature uniformity) Effective control, so as to obtain high and low temperature blackbody normal emissivity 0.98, temperature stability ≤ ± 0.15K/30min, temperature uniformity ±0.25K high-performance calibration indicators. By adding different thermal control measures to the high temperature black body and the low temperature black body, the temperature stability of the working temperature control interval required by each can be obtained. Among them, the temperature of the high-temperature black body is realized by applying a heat sheet with a reasonable cloth, while the temperature of the low-temperature black body is lower than the ambient temperature in the camera, and the temperature compensation is realized by installing a heat sink in the cold space, and then attaching the heating sheet to the heat pipe. For both high temperature blackbody and low temperature blackbody, precision platinum resistance thermometers are used to accurately monitor their temperature in real time. By reasonably arranging the position of the platinum resistance and the platinum resistance test line, the blackbody temperature measurement accuracy can be controlled within ±0.05°C. In the end, the high-stability large-aperture blackbody calibration system through the comprehensive work of various structural components, thermal control components and the main optical system to obtain the high-precision infrared temperature calibration requirements required by the load, which provides for subsequent model development. Successful engineering experience.
The SiC brazing mirror is the mirror whose blank is made by assembling together smaller SiC pieces with brazing technique. Using such kinds of joining techniques, people can manufacture large and complex SiC assemblies. The key technologies of fabricating and testing SiC brazing flat mirror especially for large aperture were studied. The SiC brazing flat mirror was ground by smart ultrasonic-milling machine, and then it was lapped by the lapping smart robot and measured by Coordinate Measuring Machine (CMM). After the PV of the surface below 4um, we did classic coarse polishing to the surface and studied the shape of the polishing tool which directly effects removal amount distribution. Finally, it was figured by the polishing smart robot and measured by Fizeau interferometer. We also studied the influence of machining path and removal functions of smart robots on the manufacturing results and discussed the use of abrasive in this process. At last, an example for fabricating and measuring a similar SiC brazing flat mirror with the aperture of 600 mm made by Shanghai Institute of Ceramics was given. The mirror blank consists of 6 SiC sectors and the surface was finally processed to a result of the Peak-to-Valley (PV) 150nm and Root Mean Square (RMS) 12nm.
There are numerous reflecting optical system designs that call for large-aperture convex surfaces, such as secondary mirror in on-axis three mirror anastigmatic (TMA). Several methods to test high accuracy hyperboloid convex surfaces are introduced separately in this paper. A kind of arrangement is chosen to test a surface with diameter of 420mm, radius of 1371mm, and conic K -2.1229. The CGH compensator for testing is designed, which is made up of illumination lens and hologram test plate with designed residual wavefront aberration less than 0.001λ (RMS). The second transmitted method that is equipped with a technical flat surface coating by Ag film in the bottom of surface mirror under test, which form an auto-collimation optical system to eliminate the aberration. The Hindle-Simpson test that requires a larger meniscus lens to compensate the optical aberration, and the designed result of optical test system is less than 0.0016λ. Contrasting the CGH compensator and the second transmitted method, the Hindle-Simpson testing method has the advantage of it is easily to manufacture and adjust; meanwhile the test result is stable and has been less affected by the environment. It has been found that the method is rational and reliable, and it can fulfill the requirement of manufacturing and testing process for hyperboloid convex mirrors.
A zerodur mirror whose aperture is 900mm is chosen to be the primary mirror of an optical system. The mirror is polished by rapid polishing and precision polishing methods relatively. The final surface figures of the mirror are as follows: the peak-to-valley value (P-V value) is 0.204λ (λ=632.8nm), and the root-mean-square value (RMS value) is 0.016λ, which meet the requirement of the optical system. The results show that the polishing process is feasible.
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