Lidar Atmospheric Measurements from the Surface of Mars
The NASA Phoenix mission to Mars landed on 25 May 2008 and operated for five months. A LIDAR on the Phoenix spacecraft provided measurements of atmospheric dust and clouds to a height of 20 km. The transmitter is based on a diode pumped, passively Q-switched, Nd:YAG laser, emitting at wavelengths 1064 nm and 532 nm, while the backscatter is recorded using both analog and photon counting data acquisition. It was operated for durations of 90 minutes or less, usually three times per day. The design and characterization of the Phoenix LIDAR will be described, and results will be presented showing the diurnal and seasonal variation of dust, clouds and precipitation in the atmosphere of Mars.
Airborne Validation of CALIPSO Data Products
The launch of the Cloud-Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) satellite in April 2006 allows the science community to study clouds and aerosols in the atmosphere using laser remote sensing. Validation flights were conducted using the Cloud Physics Lidar (CPL) as part of CC-Vex (CALIPSO- CloudSat Validation Experiment) in July-August 2006 and CLASIC (Cloud and Land Surface Interaction) project in 2007 to verify various CALIPSO data products. Results are presented to compare spatial and optical properties reported in both level 1 and level 2 CALIPSO data products to the airborne CPL. Retrievals of minimum detectable backscatter in the CALIPSO level 1 product are in good agreement with those from CPL. Cirrus cloud volume determinations are in fair agreement with CPL in many cases, except cases of thin "sub- visual" cirrus cloud tops which are not detected by CALIPSO 1 km and 5 km level 2 data products but are observed by CPL 5 km averaged data. CALIPSO 5 km extinction products were also in good agreement for cirrus clouds during both daytime and nighttime observations.
Ocean surface roughness measurements from CALIPSO and its application in air-sea gas exchange
Uncertainty associated with vertical gas exchange at ocean surface is a major contributor of uncertainty in global carbon budget assessment. The estimate of ocean carbon uptake varies from 1.1 PgC/yr to 3.3 PgC/yr as a result of difference in air-sea gas exchange estimates. High resolution lidar measurements of ocean surface roughness may lead to significant reduction in global air-sea gas exchange uncertainty. Air-sea gas transfer velocity is linearly proportional to mean square wave slopes at all wave scales (wave number ranging from 50 to 800 rad/m), especially the smaller scale waves such as capillary waves. The air-sea gas exchange is currently parameterized to wind information associated with microwave measurements (such as QuikScat and AMSR-E). Microwave measurement of ocean surface roughness is directly related to lower frequency surface waves (<50 rad/m). The link between microwave measurement and higher frequency waves is nonlinear. At shorter wavelengths (1 micron), lidar measures mean square wave slopes of all waves more directly. Thus it provides direct and accurate gas exchange information. The high resolution near surface wind speed can also be derived from the lidar ocean surface roughness measurements. The gas transfer velocity derived from mean square slopes are compared with the ones from high spatial resolution wind speed.
Synergy Derived from the "A-Train" Measurements: Retrieval of Single Scattering Albedo and Effective Aerosol Layer Height for Biomass-Burning Smoke
Despite the urgent need for aerosol layer height information over extensive spatial areas in air quality prediction and assimilation studies, the ability to obtain such information has been lacking. In this study, we present results from a new algorithm which infers aerosol layer height (ALH) and single scattering albedo (SSA) for biomass-burning smoke aerosols by merging measurements from three of the "A-Train" satellite sensors: CALIOP, MODIS, and OMI. This algorithm has been successfully applied to biomass-burning episodes over North America, Southeast Asia, and Europe. The retrieved SSA values agree reasonably with those from AERONET. Furthermore, by combining ALH information obtained along the track of CALIPSO with the retrieved SSA, extended information of ALH over wide areas can be obtained outside the CALIPSO track. Even when CALIOP data are not available, this algorithm still allows for the separation of smoke aerosols residing within the boundary layer from those elevated in the free troposphere by combining only MODIS and OMI data. Results from this study are expected to provide a better understanding of biomass-burning smoke aerosol transport and corresponding radiative effects.
Development and Field Testing of a Continuously Operating CO2 Lidar Profiling System
A ground-based 2-micron DIAL system for profiling atmospheric CO2 was developed at NASA Langley Research Center (LaRC) under the NASA Instrument Incubator Program. This system leverages 2-micron laser technology developed under a number of NASA programs to develop new solid-state YLF laser technology that provides high pulse energy, tunable, wavelength-stabilized, and double-pulsed lasers that are operable over pre-selected temperature insensitive strong CO2 absorption lines suitable for profiling of lower tropospheric CO2. It also incorporates new high quantum efficiency, high gain, and relatively low noise phototransistors, and a new receiver/signal processor system to achieve high precision DIAL measurements. The DIAL system was integrated and tested at LaRC, and then incorporated in a field experiment for evaluation. The field experiment was conducted during June-July 2008, at West Branch, Iowa, which is located at the center of a domain rich in complementary CO2 measurements. The objective of the experiment was to evaluate the accuracy and precision of the system and its ability to distinguish contents between boundary layer and free troposphere. Therefore, the experiment was co-located with other CO2 measurement setups that aid the evaluation. These setups include NOAA WBI tower with in-situ CO2 sampling sensors at 31, 99 and 379 m altitudes; NOAA airborne CO2 profiling; and radiosondes for atmospheric temperature, pressure and relative humidity profiling at the site. The lidar operations included daytime CO2 measurements to sense the well-mixed atmospheric boundary layer and overlying troposphere; day-to-night and night-to-day transitions; and night observations to capture CO2 mixing ratio differences within the boundary layer. Measurements included atmospheric CO2 spatial and temporal profiles as well as column measurements using high altitude clouds. Examples of CO2 DIAL system capability and measurements from the field experiment will be presented.
Mean Thermal Structure of the Low-Latitude Middle Atmosphere Studied Using Gadanki Rayleigh Lidar, Rocket, and SABER/TIMED Observations
The present study delineates the low-latitude thermal structure in the altitude range of 30 to 110 km using
Gadanki (13.5°N, 79.2°E) Rayleigh lidar (1998-2007), Thumba (8.5°N,77°E)
rocketsondes (1970-1991), and SABER/TIMED satellite (2002-2007) observations. This study particularly
addresses whether (1) the lidar data available only during nighttime is sufficient to study the background mean
thermal structure in 30-80 km altitude region, (2) the nonavailability of the lidar data during cloudy seasons
(monsoon) will affect the derived background mean thermal structure, and (3) any alternate satellite
observations can be used for getting the thermal structure of the middle atmosphere. The comparisons
between temperatures measured by Rayleigh lidar and SABER show good agreement, suggesting that
SABER data can be used effectively to study the mean thermal structure. The nocturnal average and diurnal
average of temperature from SABER show similar features, suggesting that data available from lidar only
during nighttime can be effectively used to study the mean background thermal structure between 30 and 80
km. Large difference between SABER and lidar observations during monsoon suggests that low data rate
available from the lidar is not sufficient to obtain the mean thermal structure during cloudy seasons. Beside
this, variations in stratopause (mesopause) height and temperature are also studied. The stratopause and
mesopause lie in the height region of 47-49 km and 97-99 km, with peak temperature of 265 K and 170 K,
respectively. Stratopause height and temperature show clear semiannual oscillation. No significant seasonal
variation is observed either in mesopause height or in temperature at this low latitude.