Fred W. Nagle

Global Moderate Resolution Imaging Spectroradiometer (MODIS) cloud detection and height evaluation using CALIOP

[1]xa0A global 2-month comparison is presented between the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and the Moderate Resolution Imaging Spectroradiometer (MODIS) for both cloud detection and cloud top height (CTH) retrievals. Both CALIOP and MODIS are part of the NASA A-Train constellation of satellites and provide continuous near-coincident measurements that result in over 28 million cloud detection comparisons and over 5 million CTH comparisons for the months of August 2006 and February 2007. To facilitate the comparison, a computationally efficient and accurate collocation methodology is developed. With the collocated MODIS and CALIOP retrievals, nearly instantaneous comparisons are compiled regionally and globally. Globally, it is found that the MODIS 1-km cloud mask and the CALIOP 1-km averaged layer product agreement is 87% for cloudy conditions for both August 2006 and February 2007. For clear-sky conditions the agreement is 85% (86%) for August (February). The best agreement is found for nonpolar daytime and the poorest agreement in the polar regions. Differences in cloud top heights depend strongly on cloud type. Globally, MODIS underestimates the CTH relative to CALIOP by 1.4 ± 2.9 km for both August 2006 and February 2007. This value of 1.4 km is obtained using the CALIOP 1 km layer products. When compared to the CALIOP 5-km products, the differences increase to −2.6 ± 3.9 km as a result of CALIOPs increased sensitivity to optically thin cirrus. When only high clouds above 5 km are considered, the differences are found to be greater than 4 km with individual comparisons having differences larger than 10 km. These large differences (>10 km) represent approximately 16% of the nonpolar high cloud retrievals (>5 km). For high clouds it is found that MODIS retrieves a cloud top height for 90% of the clouds detected by the CALIOP 5-km layer products. The large MODIS underestimates for optically thin cirrus occur for cases when MODIS reverts to a window brightness temperature retrieval instead of CO2 slicing. A systematic bias is found for marine low-level stratus clouds, with MODIS overestimating the CTH by over 1 km in dense marine stratocumulus regions. The cause of the bias was identified in the MODIS Collection 5 algorithm; an application of a modified algorithm reduced this bias.

The First 18 Months of Planetary Radiation Budget Measurements from the Nimbus 6 ERB Experiment

Abstract The Nimbus 6 satellite Earth Radiation Budget (ERB) experiment has continuously monitored the solar radiation input and the reflected shortwave and emitted longwave radiation exitance from the earth-atmosphere system since July 1975. In this paper, the planetary radiation budget parameters observed during the first eighteen months in orbit (July 1975–December 1976) are presented. The results show that the annual mean planetary albedo and longwave radiation flux are 31% and 234 W m−2> (radiative equilibrium temperature of 254 K), respectively. The earth atmosphere system is observed to be in complete radiation balance over a one-year period to within the experimental error of observation. There is an annual cycle of the mean monthly planetary net radiation which is due predominantly to the annual cycle of incoming solar radiation caused by the time variation of earth-sun distance and the suns declination. Monthly variations in outgoing longwave radiation due to variation in global cloudiness and ...

An Improvement to the High-Spectral-Resolution CO2-Slicing Cloud-Top Altitude Retrieval

Abstract An improvement to high-spectral-resolution infrared cloud-top altitude retrievals is compared to existing retrieval methods and cloud lidar measurements. The new method, CO2 sorting, determines optimal channel pairs to which the CO2 slicing retrieval will be applied. The new retrieval is applied to aircraft Scanning High-Resolution Interferometer Sounder (S-HIS) measurements. The results are compared to existing passive retrieval methods and coincident Cloud Physics Lidar (CPL) measurements. It is demonstrated that when CO2 sorting is used to select channel pairs for CO2 slicing there is an improvement in the retrieved cloud heights when compared to the CPL for the optically thin clouds (total optical depths less than 1.0). For geometrically thick but tenuous clouds, the infrared retrieved cloud tops underestimated the cloud height, when compared to those of the CPL, by greater than 2.5 km. For these cases the cloud heights retrieved by the S-HIS correlated closely with the level at which the CPL...

Computationally Efficient Methods of Collocating Satellite, Aircraft, and Ground Observations

Abstract The usefulness of measurements from satellite-borne instruments is enhanced if these measurements can be compared to measurements from other instruments mounted aboard the same or different satellite, with measurements from aircraft, or with ground measurements. The process of associating measurements from disparate instruments and platforms is referred to as collocation. In a few cases, two instruments mounted aboard the same spacecraft have been engineered to function in tandem, but commonly this is not the case. The collocation process may then become an awkward geometric problem of finding which of many observations within one dataset corresponds to an observation in another set, possibly from another platform. This paper presents methods that can be applied to a wide range of satellite, aircraft, and surface measurements that allow for efficient collocation with measurements having varying spatial and temporal sampling. Examples of applying the methods are presented that highlight the benefi...

Vertical mass and moisture structure from TIROS-N

Abstract During the First Global GARP Experiment (FGGE), global determinations of mass and moisture were made from TIROS-N (and NOAA-6) infrared and microwave sounding radiance measurements. At NESS in Washington, the meteorological data were produced operationally with a horizontal resolution of 250 km for inclusion in the FGGE level II-b data sets intended for application to large scale numerical analysis and prediction models. High horizontal resolution (50 km) sounding data sets are being produced by NESS and the Space Science and Engineering Center at the University of Wisconsin and at the NASA/Goddard Space Flight Center for special case studies of the “Special Observing Periods” of FGGE. Results are presented to display the characteristics of the sounding data at different resolutions. For the low horizontal resolution data, an evaluation is shown by comparisons of global analyses made only from satellite soundings over land and sea, and those made operationally by the National Meteorological Center, which excluded satellite sounding data over continental areas, but included all conventional data sources. For the high horizontal resolution sounding data, results are presented to demonstrate the delineation of small scale temperature and moisture features which are consistent with the meteorological processes involved.

Comparison of the MODIS Collection 5 Multilayer Cloud Detection Product with CALIPSO

CALIPSO, launched in June 2006, provides global active remote sensing measurements of clouds and aerosols that can be used for validation of a variety of passive imager retrievals derived from instruments flying on the Aqua spacecraft and other A‐Train platforms. The most recent processing effort for the MODIS Atmosphere Team, referred to as the Collection 5 scream, includes a research‐level multilayer cloud detection algorithm that uses both thermodynamic phase information derived from a combination of solar and thermal emission bands to discriminate layers of different phases, as well as true layer separation discrimination using a moderately absorbing water vapor band. The multilayer detection algorithm is designed to provide a means of assessing the applicability of 1D cloud models used in the MODIS cloud optical and microphysical product retrieval, which are generated at a 1 km resolution. Using pixel‐level collocations of MODIS Aqua, CALIOP, we investigate the global performance of multilayer cloud ...

HIS and the New CLARREO Mission

The High-resolution Interferometer Sounder (HIS) aircraft spectrometers have validated the accuracy of IR satellite instruments and helped form a foundation for the CLimate Absolute Radiance and Refractivity Observatory (CLARREO) benchmark climate mission (NRC Decadal Survey).