Evaluation of RadCalNet Output Data Using Landsat 7, Landsat 8, Sentinel 2A, and Sentinel 2B Sensors

Abstract

In 2013, the Committee on Earth Observation Satellites (CEOS) Working Group on Calibration and Validation (WGCV) Infrared and Visible Optical Sensors Subgroup (IVOS) established the Radiometric Calibration Network (RadCalNet), consisting of four international test sites providing automated in situ measurements and estimates of propagated top-of-atmosphere (TOA) reflectance. This work evaluates the ‘reliability’ of RadCalNet TOA reflectance data at three of these sites—RVUS, LCFR, and GONA—using Landsat 7 ETM+, Landsat 8 operational land imager (OLI), and Sentinel 2A/2B (S2A/S2B) MSI TOA reflectance data. This work identified a viewing angle effect in the MSI data at the RVUS and LCFR sites; when corrected, the overall standard deviation in relative reflectance differences decreased by approximately 2% and 0.5% at the RVUS and LCFR sites, respectively. Overall, the relative mean differences between the RadCalNet surface data and sensor data for the RVUS and GONA sites are within 5% for ETM+, OLI, and S2A MSI, with an approximately 2% higher difference in the S2B MSI data at the RVUS site. The LCFR site is different from the other two sites, with relative mean differences ranging from approximately -10% to 1%, even after performing the viewing angle effect correction on the MSI data. The data from RadCalNet are easy to acquire and use. More effort is needed to better understand the behavior at LCFR. One significant improvement on the accuracy of the RadCalNet data might be the development of a site-specific BRDF characterization and correction.

Radiometric Top-of-Atmosphere Reflectance Consistency Assessment for Landsat 8/OLI, Sentinel-2/MSI, PROBA-V, and DEIMOS-1 over Libya-4 and RadCalNet Calibration Sites

“…Although overall the largest number of matchups are retrieved for the LCFR site, the results for all sensors show large error bars for this site. References [23,24] also reported on the difficulty of retrieving accurate results over the LCFR site. The large variation in the calibration results obtained over this site may be related to the site's heterogeneity, including sparse vegetation.…”

Data Products, Quality and Validation of the DLR Earth Sensing Imaging Spectrometer (DESIS)

“…This good agreement is even more prominent when considering the uncertainty ranges provided by RadCalNet, as depicted in Figure 11, Figure 12 and Figure 13. To put this level of agreement into perspective, the agreement among RadCalNet, Landsat-8 and Sentinel-2 A/B is reported to be within 5 % for these sites (see [113]). For the remaining differences between RadCalNet and DESIS, up to ∼525 nm, the differences are partially due to noise.…”

Vicarious Methodologies to Assess and Improve the Quality of the Optical Remote Sensing Images: A Critical Review

“…Numerous post-launch absolute calibration techniques have been developed over the past decades; they can be broadly classified as on-board and vicarious methods [33][34][35][36][37][38][39][40][41][42][43]. On-board absolute radiometric calibration technique relies on calibration devices such as calibration lamps.…”

“…Automatic instrumentation of RadCalNet provides bottom-of-the-atmosphere (BOA) measurements and an estimate of propagated TOA reflectance and their associated uncertainties. Among the sites, the RVUS and GONA site show high accuracies in TOA reflectance measurement with 3% to 4% uncertainties, whereas the LCFR and BTCN site are less stable, and their respective uncertainties vary from 2% to 6% and from 4% to 4.5% [34,39].…”

“…Therefore, numerous satellites are being calibrated using the publicly available RadCalNet dataset [59][60][61][62]. However, there is a reported limitation in using these data as they are provided only at nadir view, causing viewing an angle effect on the non-nadir viewing sensor [34]. To address this issue, Bouvet et al suggested an approach based on simulating off-nadir TOA reflectances to match the viewing angle of the sensor of interest [40].…”