Hanlim Lee

This study validates tropospheric NO ₂ vertical column density (TropNO ₂ VCD) data from the Geostationary Environment Monitoring Spectrometer (GEMS) version 3.0 and the Tropospheric Chemistry Reanalysis version 2 (TCR-2) against Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) and Tropospheric Monitoring Instrument (TROPOMI) data at three Japanese sites: Yokosuka (urban), Fukue (rural-remote), and Cape Hedo (remote). The GEMS v3.0 dataset showed markedly improved agreement with MAX-DOAS compared to v2.0, especially at Fukue and Cape Hedo remote islands, with significantly reduced normalized mean bias from 142–319% to 8–18%. GEMS v3.0 showed agreement with MAX-DOAS observations at Yokosuka ( R = 0.75) and Fukue ( R = 0.50). It performed particularly well in autumn and winter. There were positive biases in autumn at Yokosuka (NMB = 3.5%), but negative biases in the other seasons (NMB = −0.4% to −51.2%). The reanalysis TCR-2 and aggregated TROPOMI TropNO ₂ VCD data (both at 1 × 1° resolution) showed moderate to good correlation at all three sites ( R = 0.72 at Yokosuka; R = 0.44 at Fukue; R = 0.57 at Cape Hedo). While the spatial resolution of TCR-2 (1.1 × 1.1°) precluded meaningful comparisons with MAX-DOAS at urban sites such as Yokosuka, TCR-2 exhibited lower biases than TROPOMI at Cape Hedo, which represents a background environment (NMB = 38% vs. 87%). GEMS v3.0 data effectively captured midday NO ₂ reductions at Cape Hedo, consistent with TCR-2 and MAX-DOAS, marking this as the first study to explore daytime NO ₂ decreases in remote regions using GEMS. NO ₂ loss pathways at Cape Hedo were examined using TCR-2 data and box-model simulations. NO ₂ levels from GEMS exhibited a decline between 10 AM and 3 PM in autumn, aligning with patterns from MAX-DOAS and TCR-2, with NO ₂ decay rates of 16 ± 10h from GEMS, 21 ± 5h from MAX-DOAS, and 22 ± 20h from TCR-2. The box-model NO _x budget analysis revealed that the NO ₂ + OH reaction was the dominant pathway for NO _x loss. The markedly improved agreement of GEMS v3.0 data with MAX-DOAS and TCR-2 data will allow potential exploration of the oxidizing capacity of the atmosphere over the clean marine regions, after further characterization of NO _x chemistry.

Results of a methodological case study of low-level clouds in the atmosphere using a 1064 nm fiber lidar are presented. The lidar experiment was carried out in Daejeon, Republic of Korea, in January–March 2025. The study’s primary objective was to ascertain the vertical extinction coefficient profiles pertaining to tenuous, low-altitude cloud formations via implementation of a refined Sequential Lidar Signal Processing Algorithm (SLSPA). The SLSPA incorporates statistical estimation theory to assess signal and measurement error. Cloud extinction coefficient profiles are estimated within the SLSPA utilizing the modified Klett–Fernald inversion algorithm. The SLSPA adaptation is required (a) to evaluate the accuracy of Q-switch laser-based lidar sounding signal deconvolution, (b) to mitigate the impact of the lidar form factor on measurement results, (c) to account for aerosol extinction coefficient variability within the cloud in the modified inversion algorithm (MIA), and (d) to evaluate multiple scattering effect correction in the MIA. Theoretical and experimental aspects of the modified SLSPA are considered sequentially in the present work. The experimental results presented here are based on datasets sampled from the entire array of experimental data obtained during the measurement period.

Yeonjin Jung, Junsung Park, Hyunkee Hong, Hanlim Lee, Ukkyo Jeong. Korean J. Remote Sens. 2025;41:803-11. https://doi.org/10.7780/kjrs.2025.41.5.8

Gangham Lee, Jeonghoon Kim, Dae-Il Kang, Hanlim Lee. Korean J. Remote Sens. 2025;41:709-16. https://doi.org/10.7780/kjrs.2025.41.5.1

Satellite measurements of nitrogen dioxide have been used to infer nitrogen oxide emissions, a critical component in tropospheric chemistry and pollution. New observations from the Geostationary Environmental Monitoring Spectrometer offer a breakthrough by providing a daytime record of nitrogen dioxide over Asia. Here we present the summertime diurnal patterns of nitrogen dioxide at major cities, power plant regions, and the Strait of Malacca. The Geostationary Environmental Monitoring Spectrometer data across various regions show high nitrogen dioxide in the morning which decrease in the afternoon, with varying hourly peaks, troughs, and amplitudes reflecting diurnal characteristics of local emissions and chemistry. Nitrogen oxide emissions inferred from Geostationary Environmental Monitoring Spectrometer and the Weather Research and Forecasting model coupled with Chemistry also show distinct patterns among regions: early morning peaks occur over Hanoi, Guangzhou, and Bangkok; mid-to-late morning peaks appear over Seoul and Beijing; and late afternoon peaks are noted in the Yangtze River Delta region. Top-down emissions incorporating temporal changes in the Geostationary Environmental Monitoring Spectrometer nitrogen dioxide yield the most accurate nitrogen dioxide simulations.

Nitrogen oxides (NO_x) are key precursors of tropospheric ozone and particulate matter. The sparse local observations make it challenging to understand NO_x cycling across the Tibetan Plateau (TP), which plays a crucial role in regional and global atmospheric processes. Here, we utilized Geostationary Environment Monitoring Spectrometer (GEMS) data to examine the tropospheric NO₂ vertical column density (Ω_NO2) spatiotemporal variability over TP, a pristine environment marked with natural sources. GEMS observations revealed that the Ω_NO2 over TP is generally low compared with surrounding regions with significant surface emissions, such as India and the Sichuan basin. A spatial decreasing trend of Ω_NO2 is observed from the south and center to the north over Tibet. Unlike the surrounding regions, the TP exhibits opposing seasonal patterns and a negative correlation between the surface NO₂ and Ω_NO2. In the Lhasa and Nam Co areas within Xizang, the highest Ω_NO2 in spring contrasts with the lowest surface concentration. Diurnally, a midday increase in Ω_NO2 in the warm season reflects some external sources affecting the remote area. Trajectory analysis suggests strong convection lifted air mass from India and Southeast Asia into the upper troposphere over the TP. These findings highlight the mixing interplay of nonlocal and local NO_x sources in shaping NO₂ variability in a high-altitude environment. Future research should explore these transport mechanisms and their implications for atmospheric chemistry and climate dynamics over the TP.

Seonyeong Park, Hanlim Lee, Jeonghyeon Park. Korean J. Remote Sens. 2025;41:291-300. https://doi.org/10.7780/kjrs.2025.41.2.1.4

Dagyo Lee, Wonei Choi, Hyunkee Hong, Hanlim Lee. Korean J. Remote Sens. 2025;41:387-400. https://doi.org/10.7780/kjrs.2025.41.2.1.12