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An improved scheme for Cross‐track Infrared Sounder (CrIS) geolocation assessment for all scan angles (from −48.5° to 48.5°) is developed in this study. The method uses spatially collocated radiance measurements from the Visible Infrared Imaging Radiometer Suite (VIIRS) image band I5 to evaluate the geolocation performance of the CrIS Sensor Data Records (SDR) by taking advantage of its high spatial resolution (375 m at nadir) and accurate geolocation. The basic idea is to perturb CrIS line‐of‐sight vectors along the in‐track and cross‐track directions to find a position where CrIS and VIIRS data matches more closely. The perturbation angles at this best matched position are then used to evaluate the CrIS geolocation accuracy. More importantly, the new method is capable of performing postlaunch on‐orbit geometric calibration by optimizing mapping angle parameters based on the assessment results and thus can be further extended to the following CrIS sensors on new satellites. Finally, the proposed method is employed to evaluate the CrIS geolocation accuracy on current Suomi National Polar‐orbiting Partnership satellite. The error characteristics are revealed along the scan positions in the in‐track and cross‐track directions. It is found that there are relatively large errors (~4 km) in the cross‐track direction close to the end of scan positions. With newly updated mapping angles, the geolocation accuracy is greatly improved for all scan positions (less than 0.3 km). This makes CrIS and VIIRS spatially align together and thus benefits the application that needs combination of CrIS and VIIRS measurements and products.

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Prehistoric Holocene eruptions of Changbaishan volcano in Northeast China are poorly dated, with the exception of the 946 CE Millennium eruption. Poorly refined age estimates for the earlier eruptions present problems for the reconstruction of the eruptive history of the volcano. The Qixiangzhan eruption (QE) is a major controversial event in terms of its eruptive timing (ranging from ~88 to ~4 kyr) and style (effusive or explosive). As a result of the imprecise age estimates for the eruption, a geomagnetic field excursion recorded within the QE comendite has been variably correlated with a number of different excursion events observed elsewhere. In this study, a visible early Holocene tephra was identified in Yuanchi Lake, ~30 km east of the Changbaishan volcanic vent, and was dated to 8831‐8100 cal yr BP using Bayesian age modelling. Glass shard compositions enable the correlation of this tephra with the poorly dated QE, as well as with a tephra (SG14‐1058) recorded in Lake Suigetsu, in central Japan. These correlations confirm that the QE was explosive and that the ash from the QE can serve as an important early Holocene marker bed across East Asia. In addition, we propose an age of ~8100 cal yr BP for the QE based on the precise date of the Suigetsu SG14‐1058 tephra. Our results also confirm that the geomagnetic field excursion recorded in the Qixiangzhan comendite dates to ~8100 cal yr BP.

Given the fact that Cross-track Infrared Sounder (CrIS) and the Visible Infrared Imaging Radiometer Suite (VIIRS) are currently onboard the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite and will continue to be carried on the same platform as future Joint Polar Satellite System (JPSS) satellites for the next decade, it is desirable to develop a fast and accurate collocation scheme to collocate VIIRS products and measurements with CrIS for applications that rely on combining measurements from two sensors such as inter-calibration, geolocation assessment, and cloud detection. In this study, an accurate and fast collocation method to collocate VIIRS measurements within CrIS instantaneous field of view (IFOV) directly based on line-of-sight (LOS) pointing vectors is developed and discussed in detail. We demonstrate that this method is not only accurate and precise from a mathematical perspective, but also easy to implement computationally. More importantly, with optimization, this method is very fast and efficient and thus can meet operational requirements. Finally, this collocation method can be extended to a wide variety of sensors on different satellite platforms.

The Suomi National Polar‐orbiting Partnership Program (NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) Thermal Emissive Bands (TEBs) have been performing well since the data became available on 20 January 2012, and the Sensor Data Record data reached validated maturity on 18 March 2014. While overall the validation has shown that these channels have an estimated absolute uncertainty on the order of 0.1 K based on extensive comparisons, there is a remaining issue that persisted over the years. A calibration bias on the order of 0.1 K is introduced in channels such as M15 during the quarterly blackbody temperature warm‐up/cooldown, and the bias is further amplified by the sea surface temperature (SST) retrieval algorithm up to 0.3 K in the global daily‐averaged products which causes an apparent spike in the SST time series. Our investigation reveals that this bias is caused by a fundamental but flawed theoretical assumption in the VIIRS calibration equation, which states that the shape of the calibration curve is assumed unchanged from prelaunch to postlaunch without any constrains. While the assumption may work to account for long‐term degradation, it has a shortcoming during the blackbody unsteady state. In this study, we present a diagnostic and correction method with a compensatory term (Ltrace) to reconcile the assumption such that it removes the calibration bias during the blackbody temperature changes. The methodology has been tested using historical data, and the results are very positive. The implementation has minimal impacts on the operational data processing system and is readily available for use in operations.

Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS) has been collecting global night light imaging data for more than 40 years. With the launch of Suomi-NPP satellite in 2011, the Day/Night Band (DNB) of the Visible Infrared Imaging Radiometer Suite (VIIRS) represents a major advancement in night time imaging capabilities because it surpasses DMSP-OLS in having broader radiometric measurement range, more accurate radiometric calibration, finer spatial resolution, and better geometric quality. DMSP-OLS sensor does not have on-board calibration and data is recorded as digital number (DN). Therefore, VIIRS-DNB provides opportunities to perform quantitative radiometric calibration of DMSP-OLS sensor. In this paper, vicarious radiometric calibration of DMSP-OLS at night under lunar illumination is performed. Events were selected when satellite flies above Dome C in Antarctic at night and the moon illuminates the site with lunar phase being more than quarter moon. Additional event selection criteria to limit solar and lunar zenith angle range have been applied to ensure no influence of stray light effects and adequate lunar illumination. The data from DMSP-OLS and VIIRS-DNB were analyzed to derive the characteristic radiance or DN for the region of interest. The scaling coefficient for converting DMSP-OLS DN values into radiance is determined to optimally merge the observation of DMSP-OLS into VIIRS-DNB radiance data as a function of lunar phases. Calibrating the nighttime light data collected by the DMSP-OLS sensors into radiance unit can enable applications of using both sensor data and advance the applications of night time imagery data.

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