Lelia Vann (l.b.vann@larc.nasa.gov), SAGE III Science Manager, Aerosol Research Branch, NASA Langley Research Center
A Lidar In-space Technology Experiment (LITE) Science Steering Group (SSG) meeting was conducted at the Langley Research Center (LaRC) on Friday, May 5, 1995. The purpose of this meeting was to share and discuss the LITE data analyses, research activities, and future plans, and to summarize the LITE papers to be presented at the American Geophysical Union (AGU) 1995 Spring Meeting. The LITE Principal Investigator, M. Patrick McCormick, welcomed everyone and briefly summarized the agenda and the objectives for the meeting.
The LITE Project Manager, John Rogers, presented a brief overview of the LITE mission including significant accomplishments, lessons learned, and in-flight anomalies. He outlined LITE post-flight activities leading up to a current status report. He also used selected photographs to discuss significant events concerning LITE while it was being prepared for launch at Kennedy Space Center (KSC), mission control activities at Johnson Space Center (JSC), and receptions held at JSC and LaRC.
Bill Hunt presented an overview of the LITE performance characteristics stating that early emphasis has been on identifying and characterizing baseline distortions (semi-systematic noise on the baseline). Two known types of distortion were covered: sinusoidal oscillation and ripple. Both types are potentially significant at low signal levels. Selected plots of actual LITE data were used to illustrate these distortions.
Kathy Powell presented an update on the current status of LITE data processing and discussed the future LITE data processing plans. A packet of information was distributed that contained a list of all the LITE high-rate data that were obtained during the mission and plots of the LITE high-rate data coverage along the orbit tracks. The list of all the LITE high-rate data shows the beginning and ending times, Greenwich Mean Time (GMT) and Mission Elapsed Time (MET) for each segment of LITE high-rate data and indicates which segments have been converted to the level 0, version 1 data format. The LITE level 0, version 1 data format contains time-sequenced, raw signal, backscatter profiles for each wavelength; nadir latitude and longitude of each profile; meteorological data; ephemeris data (orbiter position and attitude) obtained from the space Shuttle onboard Guidance, Navigation, and Control (GN&C) data; and a subset of the Instrument Status Data Block (ISDB).
Powell noted some limitations of the LITE level 0, version 1 data product. The latitude, longitude, and shuttle altitude parameters are approximate due to the use of the Space Shuttle onboard GN&C data. These parameters will be improved in the level 0, version 2 data product by using the ephemeris data from the PATH product. There will also be new information added to the LITE level 0, version 2 data product: latitude and longitude of the LITE footprint, the angle away from nadir to which LITE was directed, and a version identification descriptor. This next version is currently being processed and will completely replace LITE level 0, version 1.
Chip Trepte described the status and availability of meteorological products and satellite images collected during the LITE mission and acquired afterwards. He also provided a listing of the present satellite image catalog archived at Langley.
Mary Osborn reported on the LITE data distribution. A database has been created and is being maintained by Dave Woods. It identifies all reports of correlative measurements taken during LITE and all requests for LITE data. Fifty data reports and 23 specific data requests have been received to date. A summary of LITE level 0 data and analyzed data products that have been distributed was presented. Examples of correlative comparisons with Rengers down-looking lidar on the Falcon aircraft and with Stefanuttis ground-based lidar were shown as well.
A good portion of the remainder of the meeting was spent covering the AGU LITE papers. Pat McCormick, also the co-convenor of the LITE Special Session, presented a listing of all 29 papers and the Special Session agenda. The session begins with an overview of the LITE mission, which identifies the dates, times, orbits, measurements, objectives, etc. Some measurement examples are shown, e.g., super typhoon "Melissa." Richard Couch follows this overview with a brief discussion of the LITE hardware elements. Bill Hunt discusses the overall LITE data characteristics including any artifacts found to date. These introductory papers are followed by initial data use investigations. Some are summarized below, as given at the LITE SSG meeting, along with future plans for each investigator.
C. M. Platt summarized the paper entitled "Observations on tropical clouds with LITE." The talk begins with a short introduction to the importance of tropical clouds in climate, how they are formed in the upper troposphere, and our present knowledge of their distribution. This is followed by an account of the available LITE orbits over both the West and East Pacific. Measurements from these orbits show something new: the three-dimensional distribution of the clouds, their coverage, and their chief characteristics. A brief description of an algorithm developed for determination of cloud boundaries follows, together with some preliminary results on cloud height and depth statistics. These statistics highlight differences between the quiescent East Pacific compared to the active West Pacific region in the vicinity of the warm pool and the relevance of the new results to climate studies.
Geoffrey Kent summarized his paper on LITE high-cloud measurements and the interpretation of SAGE II cloud data. The SAGE II aerosol extinction data show sharp gradients in extinction near or below the tropopause. These are interpreted as being due to the presence of high-altitude clouds along the optical path from the sun to the satellite instrument. Several climatological studies have been made on clouds observed in this manner. In spite of this, we are still unclear as to the exact nature of the cloud causing the extinction changes and how the data should be interpreted. Airborne lidar and, in particular, LITE offers the chance to resolve these issues. Cloud backscatter data obtained using these instruments has been converted, using a simple model, to extinction and inverted to obtain the equivalent SAGE II extinction profiles. Initial software development was done on airborne lidar data and has recently been converted and tested on LITE data. Airborne lidar data from flights ranging over 10,000 km have been processed. To this point only a small quantity of LITE data have been studied but now that we are confident that the software is working we plan to make a study of all suitable LITE cloud data between about 30 degree N and 30 degree S. Application to the SAGE II data set will include the following:
Raymond M. Hoff summarized the paper entitled "LITE Observations of Large Scale Anthropogenic Haze." As LITE passed over the continents it observed haze emanating from urban areas. Over 40 cities worldwide have been identified in the first half of the LITE data that have been analyzed to date. These haze masses are extensive, often extending over 1000 km from their source. In one case, haze from North America is followed over three LITE orbits and matched to wind trajectory information. This is believed to be the first documented North American haze plume reaching Europe. These results are especially important since the additional light scattering from human-made aerosols has been implicated as an opposite influence to global warming.
Harvey Melfi summarized his paper entitled "Comparison of LITE and Aircraft Observations of Planetary Boundary Layer and Cloud Structure of the Atlantic Ocean." Several important points made were:
William B. Grant, representing Ed Browell, summarized two papers. The first was entitled "LITE Observations of Biomass Burning Plumes over South America, Africa, and the Southern Atlantic Ocean." Grant presented plots of case studies from Brazil and Africa coverage. LITE flew over Brazil during orbit 149. Biomass burning plumes from near the equator to near 30 degree S were observed. During orbit 146, LITE passed over Africa. Clouds obscured the view of the biomass burning aerosols north of about 4 degree S. Light aerosol loading was noted from 4 degree - 25 degree S. The aerosols were kept below 4.5 - 5.5 km by an inversion layer. It is dryer in Africa than in Brazil so the aerosol plumes rose higher in Africa.
The second paper, was entitled "Comparisons of Electra-Lidar and LITE Atmospheric Measurements near the East Coast of the U. S. and Caribbean." Fifty-shot averages were found to be useful in improving the LITE determination of aerosol scattering ratios for 30-meter vertical resolution. The Electra flight matched the LITE lidar beam path very well, as determined by the aerosol features observed. The visible scattering ratios agreed very well, and were well within the uncertainty of the measurements. The UV scattering ratios also agreed well, but there was more scatter in the data.
Syed Ismail summarized his paper entitled "Simultaneous LASE and LITE Aerosol Profile Measurements over the Atlantic." The Lidar Atmospheric Sensing Experiment (LASE), an ER-2 aircraft instrument, made LITE underflights. The data presented were LASE and LITE aerosol profile measurements over the Atlantic on September 17, 1995. The urban aerosol layers, a shallow marine layer, some cloud activity in the boundary layer, a very clean mid- and upper troposphere, and Pinatubo aerosols were observed by both systems. There was excellent agreement in the boundary layer aerosol fine structure. There were some differences in regions of clouds. However, measurements in the mid-to-upper troposphere showed no bias. Aerosol backscatter wavelength-dependence measurements in the boundary layer indicated particle sizes with less than 1 µm diameter, and the Pinatubo aerosol region data needed more averaging. Additional analysis will be conducted to examine aerosol wavelength dependence for individual boundary layer features.
J. A. Reagan summarized his paper entitled "Some Results of LITE In-flight Calibration Experiments." Ground-based and aircraft measurements were made in conjunction with LITE overpasses to calibrate the LITE 532 nm and 1064 nm channels by using LITE surface returns from selected land surface standard target areas. Spectral sunphotometer measurements were used to correct for atmospheric transmission losses. The ground reflectances were determined from spectral radiometer measurements of ground reflected solar radiance plus modeling to account for non-backscatter measurement geometries and diffuse light effects. Reagan summarized the equations for estimates of LITE calibration factors, results of ground reflectance measurements, and the relation between atmospheric and surface return calibrations.
Kevin Strawbridge summarized his paper entitled "The LITE Validation Experiment Along California's Coast," which provides two interesting case studies: aerosol transport and marine stratus clouds. Large urban plumes were identified, moving up the coastline from both San Francisco and Los Angeles on Orbit 119. Cloud-top height comparisons with LITE and cloud-top distributions obtained from the marine stratus cloud deck on Orbit 135 were also shown. Particle probe data and nephelometer data from the aircraft will help provide some closure on future collaborative work with ground-based radiometer data and optical depth calculations.
Chip Trepte summarized his paper entitled "LITE Observations of Enhanced Aerosol Distributions associated with Biomass Burning," which presents LITE observations of enhanced aerosol layers over Africa, South America, and adjoining ocean areas and examines the implications of long-range transport.
Kathy Powell presented an overview of the poster "Observations of Saharan Dust by LITE." This poster shows elevated layers of Saharan dust extending from North Africa, across the Atlantic Ocean, and into the Caribbean Ocean. The dust layers over Africa extend vertically over the entire boundary layer to altitudes exceeding 5 km. Meteorological analyses [European Centre for Medium-Range Weather Forecasts (ECMWF) trajectories of air transport] and satellite images will be correlated with LITE color-modulated plots along orbit sweeps over the Atlantic Ocean to identify the sources of enhanced aerosol detected by LITE. To illustrate this, ECMWF back trajectories of air transport that terminated along Space Shuttle Discovery orbit track 116, and LITE measurements along the same orbit track were displayed. The trajectories showed the transport of air originating from the Northwest African coastal region, the Saharan Desert, and from a region over the Atlantic Ocean. Along the orbit track, LITE measurements showed enhanced aerosol in the regions that contained air that was transported from the Saharan Desert, indicating the transport of desert dust. The LITE measurements over areas which contained air originating from the ocean did not show the same aerosol enhancement.
M. C. Pitts summarized his poster entitled "Tropospheric Aerosols off the West Coast of South America as Observed by LITE" with illustrations from Space Shuttle Discovery orbits 71, 103, & 104. The data taken from these orbits were analyzed to estimate the spatial extent of aerosol layers. The available corresponding meteorological data were also analyzed to determine possible source regions and transport of the various aerosol layers.
This concluded the summary presentations of the AGU papers. Pat McCormick briefly presented charts which were prepared for NASA Headquarters justifying a LITE-2. In support of a possible LITE-2, Richard Couch has assembled a team to assess reflight options.