The Earth Observer

--Lelia B. Vann (Lelia_Vann@gmgate.larc.nasa.gov), Executive Secretary for Lidar In-space Technology Experiment Science Team Meeting

A Lidar In-space Technology Experiment (LITE) Science Team meeting was conducted at the Langley Research Center (LaRC) on Friday, June 7, 1996. The purpose of this meeting was to share and discuss the LITE research activities, data processing and analyses, and future plans.

Principal Investigator, M. Patrick McCormick, welcomed everyone and briefly summarized the agenda and the objectives of the meeting.

NASA Headquarters (HQ) Program Manager for LITE, Robert Curran, stated that the LITE proposal for data validation and processing received excellent reviews and therefore would be partially funded this fiscal year (FY 1996). Curran was not sure that the funding would continue into FY 97, but he will strongly advocate HQ funding for at least one more year to ensure adequate data validation prior to public data release.

The LITE Science Team members in attendance presented their on-going work as summarized below.

Edward Browell, Co-Investigator from LaRC, introduced William Grant, who presented their work on global distributions of tropospheric aerosols as observed by LITE and an airborne lidar during NASA's global tropospheric experiment (GTE) from 1981 to 1994.

Jim Coakley, Co-Investigator from Oregon State University, presented the vertical structure of cloud systems as deduced from simultaneous LITE and multispectral satellite imagery data.

Chet Gardner, Co-Investigator from the University of Illinois, presented the validation of LITE stratospheric temperature and aerosol measurements which he submitted to Applied Optics in May 1996. He has obtained excellent agreement of the LITE temperature profiles from 5 to 35 km with balloon observations after compensating for aerosols, using both the 532 and 355 nm channels. Temperature residuals in the 15-30 km altitude range were as low as 2deg. C The results suggest that it may be possible to recover the tropopause altitudes from the LITE data at least in regions where the aerosol loading is not severe.

George Papen, also of the University of Illinois, presented preliminary design and modeling results for an all diode-pumped master oscillator power amplifier for water vapor DIAL systems.

Raymond Hoff, Co-Investigator from Environment Canada, presented LITE observations of anthropogenically-produced aerosols. He has detected over 50 urban area and regional aerosol haze sources in the LITE data (largely nighttime observations). The aerosol plumes from these areas agree well with air trajectory information. It is believed that aerosol mass information can be estimated for the LITE data.

Geoffrey Kent, Co-Investigator from Science and Technology Corporation, presented analyses of LITE data showing upper tropospheric aerosol (at altitudes greater than 6 km) in the southern hemisphere. It is known from previous studies of the SAGE II data set, that this aerosol exhibits seasonal variations with a maximum aerosol optical depth in local spring. A marked feature was the geographical distribution in which the aerosol was found to occur over the ocean at large distances from land.

Similar behavior is found in the LITE data set, where distinct upper tropospheric layers are seen with optical depths ranging up to 0.1. The aerosol extinction-to-backscatter ratio is found to lie between 50 and 90, compatible with the hypothesis that the aerosol source lies in the seasonal burning of biomass material in the savannah regions of southern Africa and the other southern hemisphere continents.

Harvey Melfi, Co-Investigator from the University of Maryland Baltimore Campus, could not attend but three colleagues attended the meeting and presented their ongoing studies. Geary Schwemmer from the Goddard Space Flight Center presented the comparison of Planetary Boundary Layer (PBL) statistics as derived from the LITE data and Large Aperture Scanning Airborne Lidar (LASAL) data. LASAL was the lidar system that flew on the P-3B during the LITE correlative measurement campaign.

Steve Palm and Mohan Karyampudi from Science Systems & Applications, Inc. (SSAI) presented the derivation of water vapor and temperature profiles using airborne lidar and radiometer data collected during the LITE correlative underflights. The statistics of the boundary layer height is used with the radiometric sea surface temperature to derive the profiles. Similar PBL statistics derived from LITE data in the same regions were compared with the LASAL statistics and were also used to derive the temperature and moisture profiles. The profiles were compared to dropsonde observations.

David Randall, Co-Investigator from Colorado State University, presented comparisons of the LITE data with General Circulation Model (GCM) results. The GCM produces excessive total cloudiness, but realistic cloud forcing, which suggests an excess of optically thin clouds, e.g., thin cirrus. Therefore, the distribution of thin cirrus in the model is being investigated.

John Reagan, Co-Investigator from the University of Arizona, presented an assessment and applications of LITE surface returns from selected land surface standard target areas.

Dave Winker, Deputy Project Scientist from LaRC, presented the LITE saturation database and global cloud statistics.

Kathy Powell from Science Applications International Corporation (SAIC) presented an update on the current status of LITE data processing and discussed the future LITE data processing plans. The current version of the LITE data is LITE Level 0, version 3. This version was released in March 1996. The format of version 3 is the same as version 2, but there are 2 major differences between version 2 and 3. First, time was corrected for all known latencies.

The time correction resulted in changes to all latitude, longitude, and profile backscatter altitude values. Second, the approximation to mean sea level has been improved. The version 3 geoid is formed by combining undulations from the OSU91A potential coefficient model with the corresponding reference ellipsoid. The version 2 Earth model was an ellipsoid. This change gives better approximations to the altitude values assigned to each backscatter return.

Preliminary work to determine the amount of error in the reported footprint locations and backscatter altitudes was performed. The Space Shuttle position and attitude data extracted from the Postflight Attitude and Trajectory History (PATH) product were used to calculate footprint location and profile altitude values. The PATH product reports errors of approximately 250.0 m in position and a 3 sigma uncertainty in body-axis attitude data of approximately 0.2 degrees per axis.

Applying these errors to a typical Shuttle position and attitude vector, one axis at a time, results in altitude errors of 45.0 to 190.0 m and footprint location errors of approximately 160.0 to 900.0 m. The LITE data surface elevations were compared to elevations from the Earth Resources Observation Systems (EROS) Digital Elevation Map. A section of LITE data from orbit 82 over California and Nevada with much variety in terrain was used in the comparison. The surface elevations of LITE data and the EROS digital elevations at the LITE footprint locations were in good agreement.

The next LITE data product will be Level 1, version 1. This data product will be released in January 1997 and will be available to the public. The process to create Level 1 from Level 0 includes: removing the fixed-phase baseline shape for each profile, removing the random-phase baseline oscillation for low-gain data, performing background subtraction for each profile, and truncating the profile altitude range from -5 to 40 km. Parameters to remove fixed and random phase corrections will be provided.

Paul Crain from SAIC demonstrated the LITE data access web site:

http://ARBS8.LARC.nasa.gov/LITE/litehome.html

He showed how it could be used to access color-modulated plots, metadata, and instrument status data. He also discussed future plans for both the LITE data access page and the LITE home page.

Mary Osborn from SAIC presented a summary of the support given to participants in the LITE Correlative Measurements Program. Lidar scattering ratio profiles were analyzed and sent to over 60 ground sites. Unanalyzed high-rate data have been made available to Science Team members, correlative aircraft investigators, and selected ground sites. The European LITE (ELITE) correlative measurements program was particularly successful. The Proceedings of their Final Results Workshop were published in March and show excellent agreement with the LITE data.

Osborn also presented the results of a study to determine the LITE system constant(s) for use in the calibration of LITE data. A plot of calibration factors for several LITE orbits was presented and revealed, in many cases, variations greater than 10% over an orbit. Also, the magnitude of the calibration factors decreased over the time of the mission, indicating a decrease in optical throughput. The cause of these variations is still under investigation.

Charles Trepte, from SAIC, showed a LITE video tape that was created at LaRC under his leadership. It was constructed with the FAST visualization software and highlighted LITE observations along orbits 14, 117, and the series 145-150. Copies of the video will be available in September of this year.

For the record, Robert Menzies and Martin Platt were not able to attend but have provided summaries of their ongoing research.

Menzies, Co-Investigator from the Jet Propulsion Laboratory, provided charts on the use of LITE landmark track measurements to link directional reflectance to surface wind speed.

Platt, Co-Investigator from the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia, has been working on studies in collaboration with Winker and Mark Vaughan and validation studies in collaboration with Stuart Young, CSIRO DAR, and with Osborn.

Everyone was thanked for a job well done and the meeting was adjourned.

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