Calibration Of Remote Sensors Research Articles

A thermal infrared channel field radiometer. Part I: Characterization and laboratory test

To meet the needs of the on-orbit radiometric calibration of remote sensors, the development of independent intellectual property rights of infrared radiometer, a thermal infrared channel field radiometer (TICFR) for measurements of radiance or brightness temperature are presented for in situ measurements. The design philosophy of the optical system and structure is described, and the thermal shock resistance and working environment performance were performed using a prototype in the laboratory. The results show that the TICFR has a high resistance to thermal shock and can be used in working environments ranging from − 20–50 ℃. Then, the performances of TICFR in our laboratory are deemed to be satisfactory, based on initial requirements, The electrical autonomy, the automated operation, the portability, were experimented in situ and proved to be satisfactory. To verify the accuracy of the TICFR measurements and to check the reliability of the instrument, a laboratory experiment was carried out to compare the TICFR and the CE312. The results show that TICFR is in very good agreement with the surface brightness temperatures derived by CE312. The average deviation of the surface brightness temperatures measured by the corresponding channels of the two instruments is less than 0.1 ℃, and the standard deviation is less than 0.05 ℃. These results confirm that the measurement accuracy and stability of the TICFR are similar to those of the CE312. The TICFR has important applications in the site calibration of remote sensing in the thermal infrared band.

Optical reflection characteristic-based emissivity analysis of a pyramid array flat-plate blackbody for remote sensor calibration.

The flat-plate blackbody (FPB) is the core device in infrared remote sensing radiometric calibration for providing accurate infrared radiation energy. The emissivity of an FPB is an important parameter that directly affects calibration accuracy. This paper uses a pyramid array structure based on the regulated optical reflection characteristics to analyze the FPB's emissivity quantitatively. The analysis is accomplished by performing emissivity simulations based on the Monte Carlo method. The effects of specular reflection (SR), near-specular reflection (NSR), and diffuse reflection (DR) on the emissivity of an FPB with pyramid arrays are analyzed. In addition, various patterns of normal emissivity, small-angle directional emissivity, and emissivity uniformity are examined under different reflection characteristics. Further, the blackbodies with the NSR and DR are fabricated and tested experimentally. The experimental results show a good agreement with the corresponding simulation results. The emissivity of the FPB with the NSR can reach 0.996 in the 8-14 µm waveband. Finally, the emissivity uniformity of FPB samples at all tested positions and angles is better than 0.005 and 0.002, respectively. The standard uncertainty of experimental measurement of waveband emissivity and spectral emissivity are 0.47% and 0.38% respectively, and the simulation uncertainty is 0.10%.

Research on Large-Area Blackbody Radiation Source for Infrared Remote Sensor Calibration

Research on Large-Area Blackbody Radiation Source for Infrared Remote Sensor Calibration

Freeform reflector design for uniform illumination in a space-based remote sensor calibration system.

A freeform reflector for illumination in a space-based remote sensor calibration system is designed to produce the desired patterns and improve efficiency. Owing to the excellent cosine properties and light source stability of the integrating sphere, it is widely used as the calibration source in optical remote sensing instruments. However, the light source cannot obtain uniform illumination on a large scale. Therefore, we propose a freeform reflector design for an integral sphere source, which generates an independent irradiance distribution and achieves large-scale illumination by arraying. The irradiance uniformity and efficiency obtained were greater than 98% and 90%, respectively.

Calibration and Data Quality Assurance Technical Advancements for Quantitative Remote Sensing in the DRAGON 4 Project

Robust calibration and validation (Cal and Val) should guarantee the accuracy of the retrieved information, make the remote sensing data consistent and traceable, and maintain the sensor performance during the operational phase. The DRAGON program has set up many remote sensing research topics on various application domains. In order to promote the effectiveness of data modeling and interpretation, it is necessary to solve various challenges in Cal and Val for quantitative RS applications. This project in the DRAGON 4 program aims to promote the cooperation of the Cal and Val experts from European and Chinese institutes in Cal and Val activities, and several achievements have been obtained in the advanced on-orbit optical sensor calibration, as well as microwave remote sensor calibration and product generation. The outcomes of the project have benefited the related remote sensing modeling and product retrieval, and promoted the radiometric calibration network (RadCalNet) as an international operational network for calibration, intercalibration, and validation. Moreover, this project provided local governments with a more accurate OMI NO2 data in China, which were used to study the air quality control during APEC period, Parade period and G20 period. This will be of ongoing be value for monitoring atmospheric environmental quality and formulating pollution control strategies.

Research on the Temperature Transfer Relationship Between Miniature Fixed-Point and Blackbody for On-Orbit Infrared Remote Sensor Calibration

Miniature fixed-point blackbody (MFPB) can realize the on-orbit calibration of temperatures by tracing the miniature fixed-point. This ability can effectively improve the precision and life span of earth observation systems. Researchers have verified the feasibility of the MFPB in engineering through experiments. However, the temperature relationship between the miniature fixed-point and the blackbody is unclear at present, which means that the transfer relationship between radiation temperature of space infrared radiation standard source and international temperature scale cannot be established accurately. In this article, a temperature transfer relationship between miniature fixed-point and blackbody in MFPB is established, and the temperature transfer equation (TTE) is proposed to obtain the run-off point temperature of blackbody (RPTB). The effects of heating power and ambient temperature on the temperature transfer relationship between miniature fixed-point and blackbody are investigated numerically. Retrieval results show that a linear relationship exists between the RPTB and the heating power and ambient temperature in a single fixed-point temperature range. The TTE is obtained and explained theoretically. All experimental results of the gallium fixed-point are in good agreement with this equation. Furthermore, the RPTBs are accurately predicted at gallium-stannum and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O fixed-points by TTE. The average and maximum errors are 0.0044 and 0.0063 K, respectively. The current study is of considerable importance to the development of MFPB technology and improvement of the on-orbit infrared remote sensor calibration.

On-Orbit Star-Based Calibration and Modulation Transfer Function Measurements for PLEIADES High-Resolution Optical Sensors

The accurate on-orbit radiometric calibration of optical sensors has become a challenge for space agencies who combine their efforts through international working groups such as CEOS/WGCV or WMO/GSICS with the objective of ensuring the consistency of space measurements and to reach the absolute accuracy required by increasingly demanding scientific requirements. Different targets are generally used for calibration, depending on the specific features of the sensor or spacecraft: from on-board calibration systems to ground targets, they can all profitably be characterized and modeled. Thanks to their agility, some satellites have the capability to view extra-terrestrial targets such as stars. Although the spectral irradiance of some stars is known with very high accuracy, very little work has been done on their use as an absolute reference for the calibration of remote sensors. The reason is their low irradiance, requiring a small instantaneous field of view to observe them. Moreover, their use as a calibration reference also requires a good knowledge of the instrument’s modulation transfer function (MTF). The MTF which drives the spatial quality is a major parameter for high-resolution (HR) optical remote sensors as it indicates how spatial frequencies are transmitted and weakened by the imaging system. On the other hand, stars provide ideal targets for MTF measurement as they can be assimilated to point sources. This paper proposes a method for simultaneously computing the absolute radiometric calibration of PLEIADES’ HR optical sensors and their MTF, using stars. The radiometric model is solved in Fourier space for point sources whose irradiance can be easily controlled. Results are provided for both PLEIADES satellites and compared to the official radiometric calibration and MTF. The quality of the results and the main error contributors are discussed.

Design and Characteristic Measurement of 8000 mm Large Aperture Integrating Sphere

Integrating spheres play a central role in the radiometric calibration of remote sensors. With the development of the wide field of view (FOV) remote sensors, aperture diameters of remote sensors are becoming larger and larger. To satisfy the radiometric calibration requirements of full FOV and full aperture, an 8000mm diameter large aperture integrating sphere uniform source with a variable exit port was designed and manufactured. This integrating sphere will be used for pre-launch test and radiometric calibration of remote satellites. In this paper, optical theories were used to design the output spectral radiance. The LightTools software based on ray-tracing simulation method was used to determine the best combination and distribution of inner light sources. A spectral experiment was made to verify the spectral radiance design. To reduce the influence of longtime power-on, a new characteristic measurement method was developed to obtain the radiation characteristic of the integrating sphere, which could greatly improve the measuring efficiency. This method could also be applied to measure other large aperture uniform sources. The obtained results indicate that the spatial uniformity is 98.35%, and the angular uniformity at center position is 98.78%.

Absolute calibration of the InSb analog detector based on parametric-down-conversion

Currently the two major generally radiometric calibration methods including standard radiometric source and detectors are realized by standard transfer, but it is difficult to overcome the cumulative error during its calibration processes. The new type method based on parametric down-conversion (SPDC) which is produced by the interaction of laser and nonlinear crystal can achieve no traceability absolute calibration and it has great potential applications in optical remote sensor calibration. However, the mature time-coincidence method of correaltion photons is limit to its signal processing manner which can only handle pulse signal and it cannot be realize the analog detector calibration. Therefore, These factors restrict the correlated photons pairs for analog detector calibration technology development.

Outdoor relative radiometric calibration method using gray scale targets

The radiometric calibration of remote sensors is a basis and prerequisite of information quantification in remote sensing. This paper proposes a method for outdoor relative radiometric calibration using gray scale targets. In this method, the idea of two substitutions is adopted. Sunlight is used to replace the integrating sphere light source, and gray scale targets are used to replace the diffuser. In this way, images at different radiance levels obtained outdoors can calculate the relative radiometric calibration coefficients using the least square method. The characteristics of this method are as follows. Firstly, compared with laboratory calibration, it greatly reduces the complexity of the calibration method and the test cost. Secondly, compared with the existing outdoor relative radiometric calibration of a single radiance level, it uses test images of different radiance levels to reduce errors. Thirdly, it is easy to operate with fewer environmental requirements, has obvious advantages in the rapid calibration of airborne remote sensors before or after flight and is practical in engineering. This paper theoretically and experimentally proves the feasibility of this method. Calibration experiments were conducted on the wide-view multispectral imager (WVMI) using this method, and the precision of this method was evaluated by analyzing the corrected images of large uniform targets on ground. The experiment results have demonstrated that the new method is effective and its precision meets the requirement of the absolute radiometric calibration. relative radiometric calibration, relative radiometric correction, precision evaluation, gray scale target

La Crau: A European test site for remote sensing validation

Well characterized reference sites are of major importance for the calibration of remote sensors and the validation of retrieval algorithms. A 0.4 km square zone of 'La Crau', an arid area in the South of France, is well established for the calibration of SPOT HRV sensors, and has been regularly used for a variety of remote sensing campaigns. This study reports an investigation of the potential use of a more extended area of La Crau as a validation site for lower spatial resolution satellite sensors. Sample Bidirectional Reflectance Distribution Function (BRDF) measurements were acquired over a large part of the area of La Crau during a 3-week period in July 1995. The data were analysed to provide a detailed spectral characterization of the surface of La Crau and its temporal, directional and spatial variability. The results were used to simulate the three optical channels and the 1.6 mu m channel of the ATSR-2 sensor and compared with ATSR-2 image data from the site.