A21B-0428
Comparison of MODIS and CALIPSO cloud mask
Global cloud mask is a critical parameter for the earth's climate study. Cloud mask retrieved from passive-instrument measurements, such as those from the MODIS observations, may suffer from significant uncertainties. The CALIPSO lidar measurements provide a new dimension of cloud information and are suitable for examining the cloud mask based on passive instruments. In this work, the cloud masks from the MODIS on Aqua and the CALIOP on CALIPSO are compared. The comparison results will have significance in improving the cloud retrieval algorithms based on passive instruments and will reduce the uncertainty in the earth's radiation energy budget due to the more accurate cloud information for aerosol and thin cirrus retrievals.
A21B-0429
A Comparison of Cirrus Clouds Retrieved From POLDER-3/PARASOL and MODIS/Aqua
MODIS on board Aqua and POLDER-3 on board PARASOL are two key instruments in the A-Train constellation of satellites. MODIS has 36 spectral bands with wavelength ranging from 0.41 to 14.5 μm, but makes measurement at only one direction without information about polarization. POLDER performs multidirectional measurements, of both reflectance and polarization, at nine spectral channels (from 443 to 1020 nm). The two instruments offer different, and somehow complementary, advantages for the remote sensing of microphysical and optical properties of cirrus clouds. In this study, a comparison of cirrus clouds retrieved from the two instruments is made to obtain understanding of the possibility, advantages and limitations of synergetic retrieval. First, the comparison is made between the single scattering properties of "Inhomogeneous Hexagonal Monocrystals" (IHM) used in POLDER retrieval algorithm and the ice-crystal ensemble model used for MODIS. Substantial differences are found in the scattering phase matrix. Co-located cloud mask and cloud top height retrievals are compared, with the emphasis on high and thin cirrus clouds. The optical thicknesses of cirrus clouds retrieved by POLDER are compared with those by MODIS, with and without the constraint that the cloud effective particle size retrieved by MODIS must be similar to that of IHM.
A21B-0430
Adaptive Sky: Observing Clouds Using Multi-Instrument, Multi-Platform Sensor Webs
At present there exists a large suite of spaceborne and in-situ assets operated by NASA, NOAA, and other organizations, that provide independent sensing of the Earth's atmosphere, oceans, and land surfaces. As the number of these assets grows, there is an increasing need for methods that combine these observations to provide a more complete and coherent picture of important geophysical processes. As part of a project supported through NASA's Earth Science Technology Office (ESTO), we have developed techniques that address this challenge by dynamically combining information from multiple sensors on different platforms to form sensor webs, which can respond quickly to short-lived events and provide rich, multi-modal observations of objects, such as clouds, that are evolving in both space and time. Techniques were adapted from the fields of computational data mining, computer vision, and machine learning that allow correspondence to be automatically established among various sets of observations. Two science scenarios were chosen to steer the development of the project: (1) matchups between the morning and afternoon constellations of the NASA Earth Observing System (EOS) satellites, including the MODIS, MISR, AIRS, CloudSat, and CALIPSO instruments, and (2) correspondences between satellite and ground-based cloud images. The EOS matchup scenario provided improved satellite-derived information about cloud formation and development, along with important algorithm intercomparison information. The second scenario yielded new perspectives related to the three-dimensional structure and development of clouds. This work was performed at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration.
A21B-0431
On the use of Polarization and Backscatter Features to Retrieve Liquid Water Clouds Microphysical Properties
Multiangle polarized measurements can be used to observe cloud bow together with its supernumerary bows over liquid clouds. As demonstrated by Breon and Goloub [1998], such measurements around cloud bow, are suitable to retrieve effective radius and effective variance of liquid droplets distribution. Recently the method has been applied to POLDER (Polarization and Directionality of the Earth Reflectances) data, and retrieved parameters were compared to MODIS (Moderate Resolution Imaging Spectroradiometer) retrievals using a bispectral technique [Nakajima and King, 1990], [Platnick et al, 2003]. Results of this study [Breon and Doutriaux, 2005] showed an apparent systematic discrepancy between the two techniques and conclusions were directed toward erroneous assumptions in the microphysical models used in MODIS retrievals. The A-Train mission has been providing simultaneous observations between POLDER3/Parasol and MODIS/Aqua for more than two years and it is of primary importance to understand correctly the information provided by each instrument if we aim at using both instrument in a synergistic way. We are revisiting here the use of multidirectionnal observations of cloud polarized reflectances in the backscatter direction for liquid clouds microphysical properties retrieval. Based on a variational method and a simple forward model, we present evidence that observed differences between MODIS and POLDER retrievals can be explained by taking into account cloud field heterogeneities. We show in particular that techniques using single scattering features are subject to potential biases that might not appear clearly if the assumption of homogeneous cloud is used. Based on single scattering approximation, full computation of reflectance field, and data from the MODIS and POLDER instrument we provide here an explanation to reconcile these apparently incompatible retrievals.
A21B-0432
Comparison of MODIS optical depths with CALIPSO.
One month of collocated MODIS and CALIPSO layer optical depths are compared using a newly implemented CALIPSO cloud optical depth retrieval for single layer, optically thin cirrus with the goal of evaluating the MODIS retrieved cloud optical properties. This CALIPSO retrieval algorithm can be applied to cases with an elevated cloud layer surrounded by clear air. The lidar attenuated molecular backscatter signal from above and below the layer is used to compute the layer transmittance, and hence optical depth. This methodology reduces the retrieval uncertainties by not requiring assumptions about the physical or optical properties of the cirrus. Using the retrieved optical depths, the MODIS cloud optical retrievals are evaluated. We also provide a verification of the CALIPSO layer transmittance measurement with collocated Cloud Physics Lidar (CPL) data, and data from ground based lidar instrumentation.
A21B-0433
A Study of Tropical thin Cirrus Clouds with Supervised Learning
ABSTRACT Accurate knowledge of the temporal frequency and spatial extent of optically thin cirrus is crucial to climate feedback analysis. Current global warming theory asserts that when the atmospheric concentration of CO2 increases, the outgoing longwave radiation at non-window wavelengths is reduced. If the Earth's net radiative balance is to remain stable, ground temperatures must rise in response, thereby increasing thermal emission to space. Current models do not account for subsequent changes in cloud cover, because this aspect of the climate feedback system is so poorly understood. One possible response of the cloud-climate feedback process is an increase in the global occurrence of thin cirrus clouds, driven by the increase in longwave cooling in the upper troposphere that results from higher CO2 concentrations. Exacerbating the difficulty of assessing the situation is the fact that passive remote sensing instruments cannot reliably detect cirrus clouds with optical depths less than ~0.3, because these clouds do not reflect enough sunlight to create a sufficient contrast with the Earth's surface. Now, however, the presence of thin cirrus can for the first time be accurately detected and systematically monitored by the combination of active and passive sensors onboard the CALIPSO satellite. Nevertheless, the data record is still quite limited, as CALIPSO has been in orbit for only 16 months. We have therefore initiated a multi-platform data fusion study to establish a methodology for extending the limited set of CALIPSO measurements to the existing 30-year record of passive remote sensing data, and thus improve our understanding of cloud feedback mechanisms. Using nighttime data from the first 10 days in April 2007 as a training set, we applied a general regression neural network (GRNN) to collocated samples of sea surface temperature (SST) reported by AMSR, brightness temperatures (BT) from the CALIPSO imaging infrared radiometer (IIR), and optical depths (OD) derived from the CALIPSO lidar measurements. The result is an accurate mapping of the optical depths derived from the active sensors to the brightness temperatures computed from the passive sensor measurements. Applying the trained network to this combination of passive sensor parameters, optical depths as small as 0.1 can be reliably retrieved. The relative uncertainties in the retrieval are reasonable, and can be improved significantly by use of a much larger training set.
A21B-0434
Comparisons of Aerosol-Cloud Observations Between a Ground-based Raman-Mie Lidar and CALIPSO
Global vertical profiles of aerosol and cloud are currently being observed by satellite CALIPSO. Based on the inherent properties of elastic-scattering lidar, the lidar ratio (extinction-to-backscatter ratio) becomes very important to quantitatively retrieve the distribution of aerosol/cloud extinction or backscatter coefficient. In this presentation, we examine the feasibility of using MODIS-retrieved aerosol optical depth over ocean to constrain the aerosol lidar ratio in the CALIPSO retrieval of aerosol extinction profile with Fernald algorithm, and then compare these lidar-ratios to those derived from both column measurements by the CIMEL Sunphotometer and a combination of the ground-based lidar and radiometer. We explore the variability of lidar ratios for the different types of aerosol over the US east coast. In addition, we present our validation measurements for aerosol vertical profiles. So far, 13 near simultaneous observations by our ground-based multi-wavelength Raman-Mie lidar which operated in New York City (40.821N, 73.949W), have been obtained together with other supporting measurements. In particular, comparisons of aerosol extinction profiles are performed between the ground- based lidar and CALIPSO observations and the vertical distribution of smoke plumes, aloft aerosol layer, urban aerosol and PBL height are presented and compared. Retrievals of optically thin clouds heights and optical depth in the low- and high-altitude from CALIPSO and MODIS/Aqua, respectively, are examined with respect to ground- based lidar measurements and several biases in the measurements are presented.
A21B-0435
Teleconnectivity in Upper Tropospheric Clouds and Water Vapour from the EOS Microwave Limb Sounder and their implication for the Pacific Ocean-Atmosphere Coupling System
Upper tropospheric clouds and water vapour have a large affect on the Earth's radiation budget. The NASA Earth Observing System (EOS) comprises of a series of polar orbiting satellites of which a subset is known as the A- train constellation. Close comparisons of clouds and the radiation budget may be made from A-train instruments in both space and time, with excellent precision and spatial coverage. The presence of high ice clouds (both thick cirrus and cumulonimbus) and water vapour are detected well by the GHz radiometers of the passive Microwave Limb Sounding (MLS) instrument on the EOS Aura satellite. Fluctuations in these upper tropospheric (UT) components are examined in conjunction with longwave, shortwave and albedo measurements from the Clouds and Radiant Energy System (CERES) instrument. The El Nino Southern Oscillation (ENSO) plays a key role in the natural variability of the climate system, and has strong links to A-train observations. Analysis of MLS cloud ice at UT levels is a novel and accurate measure of deep convective cores associated with the ascending branch of the Walker cell. As such, MLS retrieved clouds above 177hPa and water vapour above 316hPa were found to exhibit a significant teleconnectivity between Darwin and Tahiti. Variability in radiation budget was also detected by the CERES instrument on the Aqua and Terra satellites, not only over the Pacific, but over the entire tropical belt. Spatially gridded MLS measurements are examined using Principal Components Analysis to accurately replicate the traditional Multivariant ENSO Index. This methodology enables perturbations in the Pacific radiation budget to be estimated from cloud and water vapour variability over the ENSO cycle and a potential for back-dating upper tropospheric MLS measurements. This has implications for climate prediction, by reducing uncertainty in the climate sensitivity parameter. It also highlights strong links between the upper troposphere and surface, climate- ocean feedbacks and may enable better prediction of natural climate variability over a seasonal timescale. http://geos.ed.ac.uk/homes/s0094337/ENSO.html
A21B-0436
Temperature And Bandwidth Effect in Brewer and Dobson Direct Sun Observations
Dobson and Brewer spectrophotometer are the main instruments to monitor the ozone shield by ground based observations, and they have an important role for validation of ozone satellite data. Ground based total ozone observations from Brewer and Dobson spectrophotometers, operated at mid-latitudes stations, typically show a seasonal bias in the residual with a amplitude of a few percent. Mid-latitude total ozone trends caused by ozone depleting substances are on the order of few percents per decade. Therefore, only a maximum instrumental shift of 1% over the measured period can be tolerated for measurements to derive reliable trends. At Arosa two Dobson and three Brewers instruments have been co-located since 1992, producing a unique data set of quasi-simultaneous observations that is valuable for the study of systematic differences within the measurements. The differences can be at least partially attributed to the different sensitivities of the wavelengths used in the retrieval algorithms. This might explain different column ozone as a consequence of seasonal variability, mainly, in temperature in the lower stratosphere and in ozone slant path. The temperature dependence has been calculated using three different absorption spectra (Bass and Paur, Daumont and those used in the GOME satellite), weighing of the slit functions for each operational Brewer and for the primary standard Dobson spectrophotometers. The seasonal bias between Dobson and Brewer total ozone measurements is reduced from 3% to 1%, if one takes into account the temperature dependence of the Bass and Paur absorptions spectra and the ozone slant path effect. The accuracy and the resolution step of the experimental data of ozone cross sections have an important role. The ozone cross section must be convoluted for the slits functions that can vary from one instrument to an other, therefore the different spectra yield different results.
A21B-0437
AIRS Version 5 Trace Gas Retrievals
The Atmospheric Infrared Sounder (AIRS) currently on the EOS-Aqua platform globally retrieves profile information of several trace and minor gases from nadir viewing of IR emittance. We present new Version 5 results on ozone, carbon monoxide, methane and carbon dioxide and compare our results with near coincident measurements from the Tropospheric Emission Spectrometer and the Microwave Limb Sounder on EOS-Aura.
A21B-0438
Evaluation of the NASA Langley Research Center airborne High Spectral Resolution Lidar extinction measurements during the Megacity Initiative: Local and Global Research Observations (MILAGRO) Campaign
The NASA Langley Research Center (LaRC) airborne High Spectral Resolution Lidar (HSRL) was deployed on the NASA LaRC B-200 King Air aircraft and measured profiles of aerosol extinction, backscatter, and depolarization during the Megacity Initiative: Local and Global Research Observations (MILAGRO) Campaign in March 2006. The HSRL collected approximately 55 hours of data over 15 science flights, which were coordinated with the Sky Research J-31 aircraft (5 flights), the DOE G-1 aircraft (6 flights), and the NCAR C-130 aircraft (4 flights). This coordinated effort in MILAGRO provides the first opportunity to evaluate the HSRL aerosol extinction and optical thickness profiles with corresponding profiles derived from the other airborne measurements: 1) the 14 channel NASA Ames Airborne Tracking Sunphotometer (AATS-14) on the J-31 and the in situ nephelometer measurements of aerosol scattering and Particle Soot Absorption Photometer (PSAP) measurements of aerosol absorption from the Hawaii Group for Environment and Atmospheric Research (HiGEAR) on the C-130. This study will include comparisons of aerosol extinction from these three techniques in cases where the HSRL flew directly over the AATS-14 and HiGEAR instruments while they measured aerosol extinction profiles. The results are used in assessing the uncertainty of the HSRL extinction profiles. Column aerosol optical depth (AOD) derived from the HSRL measurements is also compared with AOD derived from Moderate Resolution Imaging Spectroradiometer (MODIS) measurements acquired on the Terra and Aqua spacecraft and from Aerosol Robotic Network (AERONET) ground-based Sun photometer measurements.
A21B-0439
Integrating retrieved cloud information with model simulation to extend usability of tracer gas retrievals.
We have explored the possibility of using retrieved cloud information to extend the usability of trace gas concentration retrievals from satellites, since choosing only cloud-free retrievals might lead to a bias in their source-sink estimates using inverse modeling, i.e. the geographic locations of cloud-free or cloudy regions and trace gas source or sink regions might be correlated. We used methane retrievals (IMAP) and cloud retrievals (FRESCO) from SCIAMACHY as an example for this study, and assumed agreement between 3D model simulations (MATCH) and cloud-free satellite retrievals as a proxy for defining usability of satellite data. We found that when the pixel is very cloudy (f>0.7), the model simulation, which is integrated with retrieved cloud top height and cloud fraction data, yields similar agreement with observations as obtained with cloud-free pixels (f=0). The addition of cloudy pixel data significantly extends the spatial and temporal coverage of methane retrievals that can be used in source and sink studies. We also tried to overlay the MODIS aerosol retrievals with SCIAMACHY methane data to test the impact of aerosols on trace gas retrievals. Since these two retrievals are somewhat orthogonal, i.e. stronger MODIS aerosol signals over the ocean, and stronger SCIAMACHY methane signals over the land, we have not found a significant correlation between these two retrievals. Other possible reasons for this result could be the different passing times of the two satellites and the wave length differences of the two retrievals.
A21B-0440
Variability in Vertical Profiles of Water Vapor Associated with African Aerosol over the Tropical Atlantic
We used four years (2003-2006) of MODIS aerosol optical depth and concurrent AIRS profiled water vapor to explore how the vertical distribution of water vapor may systematically change with outbreaks of African aerosol over the tropical Atlantic Ocean. The first step was to look for a relationship in the Barbados region using in-situ Barbados dust record and the profiled relative humidity from meteorological soundings. We extended the study to the synoptic scale in the West Indies using the MODIS and AIRS products. In the tropical Atlantic, preliminary results indicate that water vapor at 850-1000 hPa is significantly less in July on dusty days than clean days over the northeastern tropical Atlantic [5-25N, 30-20W] where African dust is predominant. In contrast, over the southeastern tropical Atlantic [15S-0, 5W-10E], where African biomass burning smoke prevails, water vapor at 600-1000 hPa is significantly higher in August on smoky days than clean days. Additionally, in January when African mixed aerosol (dust and smoke) is anomalously high over the equatorial eastern tropical Atlantic [5S-5N, 15W-5E], less water vapor is observed at two levels: 925-1000 hPa and 500-600 hPa. It is hypothesized that these results are associated with the non-hygroscopic nature of African dust, the hygroscopic properties of African smoke, and their transport pathways over the tropical Atlantic. These results are useful in the design and diagnostics of model simulations of climate effects of aerosols such as aerosol related precipitation change.
A21B-0441
Calibration and intercomparison of water vapor instrumentation used on the NSF/NCAR HIAPER aircraft
Subject of the study is the characterization of a Kahn DCS-80 water vapor calibration system and the calibration of two water vapor sensors used on research aircraft, namely a Buck Instruments B-1001 chilled mirror sensor and a MayComm Tunable Diode Laser Absorption Hygrometer. A series of Vaisala drop sondes were also characterized and compared to the aircraft instruments. In an effort to assess the precision of the water vapor sensors that are being used on board the NSF/NACR GV aircraft (HIAPER), the instruments were tested at ambient pressure (800 mbar) inside an environmental chamber to simulate temperature conditions during flight. Tested dewpoints ranged from -70 to +20 degrees Celsius. The TDL - hygrometer was calibrated in preparation for an international water vapor measurement intercomparison campaign at the Forschungszentrum Karlsruhe, Germany. We will present the detailed calibration and characterization procedure, the laboratory setup for the different sensors, results from the calibrations of all instruments, assess their precision and useful operating range, and present some preliminary results from the international intercomparison campaign.
A21B-0442
Correlation analysis between trace gases and aerosol from Satellite Remote Sensing
Recent development in satellite remote sensing, with its global coverage now enables us to investigate correlation between aerosol and pollutant gases. MOPITT (Measurement of Pollution in the Troposphere) onboard Terra satellite launched in December of 1999 has observed carbon monoxide density, and MODIS (Moderate Resolution Imaging Spectroradiometer) has observed AOD (Aerosol Optical Depth). In addition, SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) and OMI have observed sulfur dioxide and nitrogen dioxide density. Increase of pollutant gases in tropospheric atmosphere modifies chemical, physical, and climatological properties. Aerosol classification algorithm by using MODIS AOD and OMI AI data is used to investigate correlation between gases and aerosols. This study investigates correlation between aerosol and pollutant gases which are regarded as a precursor of aerosol, and their dependence on season, and region. To investigate regional dependence, we divided globes into 7 areas – North America, South Africa, Europe, North Africa, South Africa, Asia, and Australia. Correlation between black carbon AOD retrieved by MODIS-OMI aerosol classification algorithm and CO becomes better than that between fine mode AOD and CO in most regions. By comparing these results with MODIS fire counts, enhanced correlations are found for CO with black carbon aerosol in the region of biomass burning and wild fires. But the correlation between SO2 and sulfate AOD is not good because of longer time in converting SO2 into sulfate.
A21B-0443
Height Resolved Ozone Climatologies in the Arctic Winter Based on Ozone Sounding and GOMOS/Envisat Profiles
Ozone climatologies are useful e.g. in satellite retrieval algorithms and for atmospheric modeling purposes. Due to various principles, resolution and geometry of column ozone measurements, it is not straightforward to compare ozone soundings with either ground based or satellite data. Furthermore, during the last years the height domain of global chemistry coupled climate models has increased significantly. In order to study the performance of a model in describing e.g. the polar vortices a high resolution ozone profile climatology is needed. As the GOMOS (Global Ozone Monitoring by Occultation of Stars) profiles are night-time measurements the data is especially valuable for this purpose. A height resolved climatology is also useful in ozone sonde studies as a residual ozone climatology (improving the total ozone estimation from sonde profiles). Star occultation remote sensing used in GOMOS/Envisat and ozone sondes are unique tools for obtaining high resolution ozone profiles from the ground to the upper mesosphere (100 km) in the polar winter. Quality controlled profiles of the GOMOS and Arctic ozone soundings were used to form a height resolved ozone climatology for the polar winter atmosphere. As a first application the climatology was tested in supplementing the ozone sonde profiles above the balloon burst point. A case study with soundings from Sodankylä is shown. The total column ozone data obtained in this way is compared to both ground based and satellite (OMI/EOS-Aura) data.