Satellite Remote Sensing
Satellites can provide nearly global coverage of the Earth with spatial resolutions and repetition rates that vary from one platform to another. Remote sensing research in the lab includes the use of satellite-measured radiances for estimating geophysical quantities such as atmospheric water vapor, trace gases, aerosol particles, clouds, and precipitation. In addition, satellite data are used to study the radiative and dynamical processes that affect the climate of the Earth.
In addition to activities with previous generation of satellite sensors (AVHRR, TOMS, SSM/I), lab scientists are working with a number of new state-of-the-art satellite instruments launched on recent Earth Observing System (EOS) platforms, including the MOderate Resolultion Imaging Spectroradiometer (MODIS) flown on NASA Terra and Aqua, and Landsat 7. In addition, lab members have project and deputy project scientist roles with SORCE and Aqua platforms, respectively. Laboratory scientists are also participating in the design of future satellite instruments and projects.
Specific satellite remote sensing activites in the laboratory include:
Operational MODIS cloud and aerosol products, and related research activities.
Satellite observations are used to study the distribution of ozone and water vapor. These trace gases have a significant greenhouse effect. Ozone affects the intensity of the UV radiation on the Earth's surface. Ozone measurements from the TOMS ultraviolet radiometer on NASA's Nimbus 7 satellite are being collected and compared with ozone measurements from the TOVS infrared radiometer on NOAA's weather satellites, and the ground-based Dobson ozone spectrometer network.
Satellite observations made with the multispectral, dual-polarization microwave radiometers, SMMR and SSM/I, have enabled the mapping of columnar water vapor distribution over the global oceans since 1979. In addition, upper air water vapor is observed in the 6.7 micrometer band from NOAA polar orbiters. These measurements have revealed new information regarding the evolution and development of events such as El Nino Southern Oscillations, consistent with results based on in situ and analyzed data. Analysis of the microwave data also has yielded valuable information on rainfall rates over the oceans.
NOAA-AVHRR data are used for remote sensing of biomass burning in the tropics, to study the interaction of smoke particles with clouds, and the impact of the smoke particles and the associated trace gases on climate. Fires are detected in the 3.75 micrometer channel, aerosol concentration and cloud reflectance in the 0.64 micrometer channel. Cloud drop size is derived from the cloud reflectance in the 3.75 micrometer channel. Using the ratio between the emission of aerosol particles and trace gases, the remotely sensed aerosol is used to estimate the total emission of trace gases. Satellite observations of the effect of smoke particles on thousands of cumulus and stratocumulus clouds in the Amazon basin showed that smoke reduced the cloud drop size by 40 percent. In contrast, to the increase in cloud albedo observed along ship tracks, the albedo of these clouds decreased.
High-resolution satellite data (Landsat) are used to detect the spatial properties of broken cloud fields. These properties are important for the understanding of radiative processes in clouds. For example, in an analysis of the distribution of cloud area, it was found that the cloud field can be described by two power functions. This finding can provide a useful tool for classification of clouds.
Multi-channel, 1Km resolution NOAA-AVHRR data sets are collected and archived in the lab for use in the retrieval of cloud parameters. The present cloud cover processing system utilizes all five AVHRR channels to provice cloud amount, cloud optical thickness, cloud top temperature, and an index indicative of the phase and size of the cloud particles. These parameters provide the basic information needed to develop models of cloud processes, which ultimately will be incorporated into climate models.
Contact: Steven Platnick