Seung-Hee Ham

Possibility of the Visible-Channel Calibration Using Deep Convective Clouds Overshooting the TTL

Abstract The authors examined the possible use of deep convective clouds (DCCs), defined as clouds that overshoot the tropical tropopause layer (TTL), for the calibration of satellite measurements at solar channels. DCCs are identified in terms of the Moderate Resolution Imaging Spectroradiometer (MODIS) 10.8-μm brightness temperature (TB11) on the basis of a criterion specified by TB11 ≤ 190 K. To determine the characteristics of these clouds, the MODIS-based cloud optical thickness (COT) and effective radius (re) for a number of identified DCCs are analyzed. It is found that COT values for most of the 4249 DCC pixels observed in January 2006 are close to 100. Based on the MODIS quality-assurance information, 90% and 70.2% of the 4249 pixels have COT larger than 100 and 150, respectively. On the other hand, the re values distributed between 15 and 25 μm show a sharp peak centered approximately at 20 μm. Radiances are simulated at the MODIS 0.646-μm channel by using a radiative transfer model under homoge...

Assessment of the Quality of MODIS Cloud Products from Radiance Simulations

Abstract Observations made by the Moderate Resolution Imaging Spectroradiometer (MODIS), the Atmospheric Infrared Sounder (AIRS), the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), and CloudSat are synergistically used to evaluate the accuracy of theoretical simulations of the radiances at the top of the atmosphere (TOA). Specifically, TOA radiances of 15 MODIS bands are simulated for overcast, optically thick, and single-phase clouds only over the ocean from 60°N to 60°S, corresponding to about 12% of all the MODIS cloud observations. Plane parallel atmosphere is assumed in the simulation by restricting viewing/solar zenith angle to be less than 40°. Input data for the radiative transfer model (RTM) are obtained from the operational MODIS-retrieved cloud optical thickness, effective radius, and cloud-top pressure (converted to height) collocated with the AIRS-retrieved temperature and humidity profiles. In the RTM, ice cloud bulk scattering properties, based on theoretical s...

Effects of 3‐D clouds on atmospheric transmission of solar radiation: Cloud type dependencies inferred from A‐train satellite data

Three-dimensional (3-D) effects on broadband shortwave top of atmosphere (TOA) nadir radiance, atmospheric absorption, and surface irradiance are examined using 3-D cloud fields obtained from one hours worth of A-train satellite observations and one-dimensional (1-D) independent column approximation (ICA) and full 3-D radiative transfer simulations. The 3-D minus ICA differences in TOA nadir radiance multiplied by π, atmospheric absorption, and surface downwelling irradiance, denoted as πΔI, ΔA, and ΔT, respectively, are analyzed by cloud type. At the 1 km pixel scale, πΔI, ΔA, and ΔT exhibit poor spatial correlation. Once averaged with a moving window, however, better linear relationships among πΔI, ΔA, and ΔT emerge, especially for moving windows larger than 5 km and large θ0. While cloud properties and solar geometry are shown to influence the relationships amongst πΔI, ΔA, and ΔT, once they are separated by cloud type, their linear relationships become much stronger. This suggests that ICA biases in surface irradiance and atmospheric absorption can be approximated based on ICA biases in nadir radiance as a function of cloud type.

Vertical-Homogeneity Assumption Causing Inconsistency Between Visible- and Infrared-Based Cloud Optical Properties

A possible cause of radiative inconsistency between visible- and infrared (IR)-based optical properties is examined and corrected for. This study is motivated by significant IR modeling biases of around -7 K found in our previous study. In that study, the model simulation was conducted using cloud optical thickness (COT) and effective radius retrieved from the Moderate-Resolution Imaging Spectroradiometer, and cloud top and base heights measured by CloudSat. For single-layered and relatively optically thick clouds (COT >; 10 ), uncertainties in the COT and effective radius are shown to have a small contribution to the IR modeling biases; making an assumption that the clouds are vertically homogeneous seems to cause most of the IR modeling biases. By creating a cloud extinction profile from the CloudSat data, IR modeling biases are reduced to -2 K instead of - 7 K.

Post-flight radiometric calibration of the Korean geostationary satellite COMS meteorological imager

The first Korean geostationary satellite, the Communication, Ocean, Meteorological Satellite (COMS) carries the Meteorological Imager (MI) that measures solar radiance at 0.675 μm and infrared (IR) brightness temperatures at four spectral bands centered at 3.8, 6.7, 10.8, and 12.0 μm. This study reports the calibration status of the COMS MI solar and four IR channels, based mainly on a comparison with Moderate Resolution Imaging Spectroradiometer (MODIS) measurements. The results obtained from four months of COMS MI solar channel measurements demonstrate that the solar channel has a dark bias of about 9–10%. On the other hand, the four IR channels appear to be well-calibrated as evidenced by a high correlation and near-unity slope between COMS and MODIS data. Nevertheless, existing biases of tenths of a kelvin are still considered to be substantial. Overall, the interpretation of COMS-derived meteorological products should take into account some uncertainty caused by possible calibration errors.

Examining impacts of mass‐diameter (m‐D) and area‐diameter (A‐D) relationships of ice particles on retrievals of effective radius and ice water content from radar and lidar measurements

Mass-diameter (m-D) and projected area-diameter (A-D) relations are often used to describe the shape of nonspherical ice particles. This study analytically investigates how retrieved effective radius (r eff ) and ice water content (IWC) from radar and lidar measurements depend on the assumption of m-D [m(D) = a D b ] and A-D [A(D) = γD s ] relationships. We assume that unattenuated reflectivity factor (Z) and visible extinction coefficient (k ext ) by cloud particles are available from the radar and lidar measurements, respectively. A sensitivity test shows that r eff increases with increasing a, decreasing b, decreasing γ, and increasing δ. It also shows that a 10% variation of a, b, γ, and δ induces more than a 100% change of r eff . In addition, we consider both gamma and lognormal particle size distributions (PSDs), and examine the sensitivity of r eff to the assumption of PSD. It is shown that r eff increases by up to 10% with increasing dispersion (μ) of the gamma PSD by 2, when large ice particles are predominant. Moreover, r eff decreases by up to 20% with increasing the width parameter (ω) of the lognormal PSD by 0.1. We also derive an analytic conversion equation between two effective radii when different particle shapes and PSD assumptions are used. When applying the conversion equation to nine types of m-D and A-D relationships, r eff easily changes up to 30%. The proposed r eff -convertion method can be used to eliminate the inconsistency of assumptions that made in a cloud retrieval algorithm and a forward radiative transfer model.

Impact of Ice Cloud Microphysics on Satellite Cloud Retrievals and Broadband Flux Radiative Transfer Model Calculations

AbstractIce cloud particles exhibit a range of shapes and sizes affecting a cloud’s single-scattering properties. Because they cannot be inferred from passive visible/infrared imager measurements, assumptions about the bulk single-scattering properties of ice clouds are fundamental to satellite cloud retrievals and broadband radiative flux calculations. To examine the sensitivity to ice particle model assumptions, three sets of models are used in satellite imager retrievals of ice cloud fraction, thermodynamic phase, optical depth, effective height and particle size, and in top-of-atmosphere and surface broadband radiative flux calculations. The three ice particle models include smooth hexagonal ice columns (SMOOTH), roughened hexagonal ice columns, and a two-habit model (THM) comprised of an ensemble of hexagonal columns and 20-element aggregates. While the choice of ice particle model has a negligible impact on daytime cloud fraction and thermodynamic phase, the global mean ice cloud optical depth retri...

Arctic Radiation-IceBridge Sea and Ice Experiment: The Arctic Radiant Energy System during the Critical Seasonal Ice Transition

AbstractThe National Aeronautics and Space Administration (NASA)’s Arctic Radiation-IceBridge Sea and Ice Experiment (ARISE) acquired unique aircraft data on atmospheric radiation and sea ice properties during the critical late summer to autumn sea ice minimum and commencement of refreezing. The C-130 aircraft flew 15 missions over the Beaufort Sea between 4 and 24 September 2014. ARISE deployed a shortwave and longwave broadband radiometer (BBR) system from the Naval Research Laboratory; a Solar Spectral Flux Radiometer (SSFR) from the University of Colorado Boulder; the Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) from the NASA Ames Research Center; cloud microprobes from the NASA Langley Research Center; and the Land, Vegetation and Ice Sensor (LVIS) laser altimeter system from the NASA Goddard Space Flight Center. These instruments sampled the radiant energy exchange between clouds and a variety of sea ice scenarios, including prior to and after refreezing began. The most c...

Simulation of Fifteen MODIS Bands for the Assessment of MODIS Cloud Products

Radiances at fifteen bands are simulated from the operational MODIS-retrieved cloud optical thickness, effective radius, and cloud top pressure collocated with the AIRS-retrieved temperature and humidity profiles for the assessments of MODIS cloud products.

Assessment of the calibration performance of Meteosat-8/9 and MTSAT-1R visible channels using cloud targets (Withdrawal Notice)

This paper was presented at the SPIE conference indicated above and has been withdrawn from publication at the request of the authors.