Search

The Radiometric Calibration Network (RadCalNet) has been established by the Committee on Earth Observation Satellites (CEOS) Working Group on Calibration and Validation (WGCV) Infrared and Visible Optical Sensors Subgroup (IVOS) in 2013 and is open to public since July 2018. The RadCalNet consists of four international test sites providing automated in situ measurements and estimates of propagated top-of-atmosphere (TOA) reflectance (Bouvet et al. 2019). This work based on the work of Alhammoud et al. (2019) for the Sentinel-2/MSI validation; and on the work of Jing et al. (2019) to correct the directional effect. In this study we extend Alhammoud et al. (2019) analysis over RadCalNet up to 2021, instead of 2018. In addition, we will present the results of a cross-mission intercomparison over RadCalNet sites for MSI-A, MSI-B and OLI-8 using DIMITRI-Toolbox. The results confirm the viewing angle effect in the Sentinel-2 data at the RVUS and LCFR sites. The correction of the directional effect improves the results over the ratios of the individual orbits by up to 5% -10%, while the average ratios has been improved by barely about 1%. However the intercomparison results illustrate the relevance of RadCalNet dataset for the vicarious validation activity. Alhammoud et al. Sentinel-2 Level-1 Radiometry Assessment Using Vicarious Methods from DIMITRI Toolbox and Field Measurements From RadCalNet Database. IEEE JSTAR, 2019, Vol: 12(9) Bouvet et al. RadCalNet: A Radiometric Calibration Network for Earth Observing Imagers Operating in the Visible to Shortwave Infrared Spectral Range. Remote Sens. 2019, 11, 2401. https://doi.org/10.3390/rs11202401 Jing et al. Evaluation of RadCalNet Output Data Using Landsat 7, Landsat 8, Sentinel 2A, and Sentinel 2B Sensors. Remote Sens. 2019, 11, 541.

A compact and portable diode-laser spectrometer is developed for high-precision measurements of the (CO2)-C-13 /(CO2)-C-12 isotope ratio. Ro-vibrational transitions belonging to different combination bands, around 2.008 mum, are detected for the two isotopomers, using wavelength-modulation spectroscopy with first-harmonic detection. The determination of the isotope ratio is performed through a comparison between the spectra, simultaneously acquired in two different multiple-reflection cells designed to contain the sample and reference gases. The reproducibility of our method is extensively investigated over different time scales. In particular, the short-term precision of the isotope ratio determination is found to be 0.03%. We discuss the presence of possible systematic shifts in the delta-value and optimise the operating conditions to ensure accuracy within the precision level. A possible use for in-situ measurements in volcanic gases is also discussed.