Vicarious calibration and validation techniques are important tools to ensure the long-term stability and inter-sensor consistency of satellite sensors making observations in the solar-reflective spectral domain. Automated test sites, which have continuous in situ monitoring of both ground reflectance and atmospheric conditions, can greatly increase the match-up possibilities for a wide range of space agency and commercial sensors. The Baotou calibration and validation test site in China provides operational high-accuracy and high-stability vicarious calibration and validation for high spatial resolution solar-reflective remote-sensing sensors. Two sites, given the abbreviations BTCN (an artificial site) and BSCN (a natural sandy site), have been selected as reference sites for the Committee on Earth Observation Satellites radiometric calibration network (RadCalNet). RadCalNet requires sites to provide data in a consistent format but does not specify the required operational conditions for a RadCalNet site. The two Baotou sites are the only sites to date that make spectral measurements for their continuous operation. One of the core principles of RadCalNet is that each site should have a metrologically rigorous uncertainty budget which also describes the site’s traceability to the international system of units, the SI. This paper shows a formalized metrological approach to determining and documenting the uncertainty budget and traceability of a RadCalNet site. This approach follows the Guide to the Expression of Uncertainty in Measurement. The paper describes the uncertainty analysis for bottom-of-atmosphere and top-of-atmosphere reflectance in the spectral region from 400 to 1000 nm for the Baotou sites and gives preliminary results for the uncertainty propagating this to top-of-atmosphere reflectance.

Background and Objectives: Depth perception of the human visual system in three-dimensional (3D) space plays an important role in human–computer interaction and artificial intelligence (AI) areas. It mainly employs binocular disparity and motion parallax cues. This study aims to systemically summarize the related studies about depth perception specified by these two cues. Materials and Methods: We conducted a literature investigation on related studies and summarized them from aspects like motivations, research trends, mechanisms, and interaction models of depth perception specified by these two cues. Results: Development trends show that depth perception research has gradually evolved from early studies based on a single cue to quantitative studies based on the interaction between these two cues. Mechanisms of these two cues reveal that depth perception specified by the binocular disparity cue is mainly influenced by factors like spatial variation in disparity, viewing distance, the position of visual field (or retinal image) used, and interaction with other cues; whereas that specified by the motion parallax cue is affected by head movement and retinal image motion, interaction with other cues, and the observer’s age. By integrating these two cues, several types of models for depth perception are summarized: the weak fusion (WF) model, the modified weak fusion (MWF) model, the strong fusion (SF) model, and the intrinsic constraint (IC) model. The merits and limitations of each model are analyzed and compared. Conclusions: Based on this review, a clear picture of the study on depth perception specified by binocular disparity and motion parallax cues can be seen. Open research challenges and future directions are presented. In the future, it is necessary to explore methods for easier manipulating of depth cue signals in stereoscopic images and adopting deep learning-related methods to construct models and predict depths, to meet the increasing demand of human–computer interaction in complex 3D scenarios.

To meet the increasing metrology demand of spectral irradiance in the short UV spectral range, a new spectral irradiance scale from 200 to 400 nm was realized at National Institute of Metrology (NIM) based on a high-temperature blackbody BB3500M, and a group of stable deuterium lamps are used as the transfer standards. Accurate real-time temperature of a blackbody is derived to reduce the temperature drift during the measurement period. A combination of an absolute and relative measurement system is designed to reduce repeatability uncertainty, and a selective optical filter method is used to remove fluorescence with a peak at 330 nm. A seven-point bandwidth novel correction method based on differential quadrature formula is put forward to correct the bandwidth error of the monochromator. The expanded uncertainties of the new spectral irradiance scale are 5.3% at 200 nm, 1.8% at 250 nm, 1.9% at 330 nm, and 3.6% at 400 nm, respectively. In the overlap wavelength from 250 to 400 nm, the average deviation between two types transfer standards, deuterium lamps and tungsten halogen lamps, is verified to be 0.39%, which are consistent with the associated measurement uncertainties.

Main text: This report describes the Key Comparison of the Consultative Committee for Photometry and Radiometry CCPR-K1.a.2017 for Spectral Irradiance in the wavelength range of 250 nm to 2500 nm. Tungsten quartz halogen lamps of the FEL type (1000 W) were used as artefacts. Each participant used its own set of lamps. The star scheme of measurements was applied with the sequence participant - pilot - participant. Twelve National Metrology Institutes participated in the comparison. Each participant's measurement data were based on a totally independent spectral irradiance scale realisation. VNIIOFI (the Russian Federation) served as a pilot. The measurements were carried out from 2017 - 2020. The analysis of the comparison was performed following the step-by-step approach described in Appendix B of the Guidelines for CCPR Key Comparison Report Preparation (CCPR-G2 Rev.4). The key comparison reference values (KCRV) were calculated independently at each wavelength as the weighted means with cut-off. The measurement data of all participants were used for the KCRV excluding just a few outliers in the wavelength range of 1700 nm to 2500 nm. The relative uncertainties of the KCRV were minimal, 0.08 %, at the wavelengths of 900 nm to 1500 nm and increasing towards the limits of the spectral range up to 0.28 % at 250 nm and 0.20 % at 2500 nm. Consistency checks were satisfied at 17 of the 28 measured wavelengths, but failed at 11 wavelengths, mostly in the infrared range. For the latter wavelengths the Mandel-Paule method was applied resulting in an additional uncertainty that varied depending on wavelength from 0.11 % to 0.89 %. In general, the measurement uncertainties submitted by the participants in this comparison were less than those submitted in the previous CCPR-K1.a comparison. This is evidenced by the values of the cut-off, which had decreased at all wavelengths by a factor of 1.2 to 3.0 depending on wavelength. However, only for seven participants the degrees of equivalence do not exceed the expanded uncertainties at almost all wavelengths. About 80 % of all results (all participants at all wavelengths) agree with the KCRV within 1 % over the whole spectral range and within 0.7 % in the visible, which is comparable with the results of the previous CCPR-K1.a comparison. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCPR, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

We have proposed a novel method for the spectral irradiance measurement of the standard lamp. The measurement has been realized by using national primary scale based on a large area WC-C fixed point blackbody for the first time. The wavelength range is from 450 nm to 1000 nm. The spectral irradiance of the standard lamp has been measured based on the traditional variable temperature blackbody and large area WC-C fixed point blackbody. The results of the two methods agree within the uncertainties. Compared with the traditional measurement method, the fixed point method can reduce the major component of the spectral irradiance measurement uncertainty related to the temperature measurement.

The emissivity of the blackbody is a very important parameter in spectral radiance measurement systems. In the conventional method, the emissivity is calculated based on the isothermal model. However, the actual temperature distribution in the blackbody cavity is always nonisothermal; the emissivity calculated based on the isothermal model may not accurately present the radiation characteristic of the blackbody. In this study, the actual temperature distributions of two blackbodies (one has an extended cone shape, and the other a 65-mm diameter cylindrical shape) are measured, and the emissivities are calculated accordingly based on the nonisothermal model at a certain temperature (873 K). The results show there are different tendencies of temperature distributions in the two blackbodies. When compared with the isothermal model, the emissivities in the 873 K temperature and 2.0–20.0 µm wavelength condition are about 1.75% and 0.18% lower at the nonisothermal model for the extended cone shape and cylindrical blackbodies, respectively. To improve the emissivity, different types of apertures are customized for the two blackbodies. For the extended cone-shaped blackbody, the emissivity in the 873 K temperature and 2.0–20.0 µm wavelength condition increases by 1.12% when using a ring-shaped graphite aperture in the cavity, whereas for the cylindrical-shaped blackbody, the emissivity in the same condition increases by 0.09% when using a high-reflective aperture in front of the cavity opening. Different from previous studies, this study provides new insight in calculating and improving the effective emissivity of blackbodies by using the measured temperature in the cavity based on the nonisothermal model.