|
|
An important Branch activity is the development and application of remote sensing techniques to parameters of the
troposphere. The development of new lidar systems to meet the needs of the meteorological community is the primary activity.
Such systems include Scanning Raman Lidar, Large Aperture Scanning Airborne Lidar, Cloud Lidar,
Micro Pulse Lidar,
GLOW and
HARLIE.
The Holographic Airborne Rotating Lidar
Instrument Experiment (HARLIE) was built to
investigate the feasibility of using Holographic Optical Element
s (HOE) as an alternative to traditional optics in a lidar
system. HARLIE is an innovative and compact lidar that uses
a novel technique to measure aerosol backscatter profiles
and is capable of scanning in a conical fashion, affording a
unique view of the atmosphere. HARLIE is designed for use
aboard an aircraft; however, it has been used extensively
over the past few years as a ground-based lidar, participating
in several field campaigns.
GLOW stands for Goddard Lidar Observatory for Wind.
It is a mobile Doppler lidar system based on double edge direct detection
technology. It consists of a molecular system at 355nm and a aerosol
system at 1064nm.
GLOW merges atmospheric science with innovative new remote sensing methodologies.
New lidar technologies are perfected during ground use in preparation for eventual
use in air and space based wind measurement systems.
.
Because of its importance in radiative transfer, convection, general circulation, and the hydrological cycle, atmospheric
water vapor plays a crucial role in understanding atmospheric processes. For example, since water is the most active infrared
molecule in the atmosphere, water vapor response is a major factor in any global warming triggered by increasing carbon
dioxide. In addition, atmospheric aerosols also have a significant impact on the earth's climate by scattering and absorbing solar
radiation and by altering the physical and radiative properties of clouds. A Scanning Raman Lidar was developed and is used to
provide the frequent and accurate measurements of water vapor and aerosols to study these atmospheric processes. For this
system, laser scattering by water vapor, nitrogen, and oxygen molecules is detected as a function of altitude. Water vapor
mixing ratio, which is the ratio of the mass of water vapor to the mass of dry air, is computed from the ratio of the Raman
scattering from water vapor and nitrogen. When combined with measurements of temperature, the lidar water vapor data gives
profiles of relative humidity. The lidar water vapor data acquired during field experiments have been used to validate radiative
transfer models and study atmospheric features such as fronts and gravity waves. The water vapor measurements also assess
the quality of ground, balloon, and space-based sensors. 
These water vapor data have been used to determine how advanced
statistical techniques (spectral, multifractal, and wavelet analysis) can be used to help understand the nature and causes of
atmospheric structure and variability. In addition to measuring water vapor, the Scanning Raman Lidar simultaneously measures
both aerosol backscattering and extinction. Figure 13 shows an example of simultaneous water vapor mixing ratio, relative
humidity, aerosol backscattering and extinction profiles. In addition to measuring aerosols in the lower troposphere, the lidar
system has also been used to measure profiles of the stratospheric aerosols produced by the June 1991 eruption of Mt.
Pinatubo. Temperature profiles in the upper troposphere and lower stratosphere are also derived from the lidar measurements.
Boundary Layer Lidar
The Large Aperture Scanning Airborne Lidar (LASAL) recently flew on NASA's P3-B in support of the Langley
Research Center Lidar In-Space Technology Experiment (LITE). LASAL primarily studies of boundary layer dynamics,
particularly the height of the planetary boundary layer (PBL), entrainment zone thickness, cloud heights and coverage, and lifting
condensation levels.
Figure 14 (click to enlarge)is an image of laser backscatter from atmospheric aerosols and clouds from LASAL and LITE.
It extends from 24.43- N, 25.58- W to 13.01- N, 17.93- W off the west coast of north Africa. Levels of scattering are color
coded using black for low scattering, then going through blue, green, magenta, orange, and white for the highest scattering
levels. The planetary boundary layer (PBL) is the region of increased aerosol scattering indicated by red and white near the
ocean surface. Clouds are indicated by the regions of strong scattering at the top of the PBL (or at other altitudes) with a
vertical "shadow" below them. The broad area of aerosol scattering between 1.5 and 5 km altitude is a layer of Saharan dust,
lofted to these altitudes during the daytime, and advected over the ocean by the trade winds. Data such as these are used to
develop algorithms to derive boundary layer heights, lifting condensation level and entrainment zone thickness. In combination
with other remotely sensed data, water vapor and potential temperature profiles within the boundary layer can be derived.
These parameters help determine the latent and sensible heat flux between the ocean and the atmosphere.
Edge Technique Wind Lidar
The objective of this program is to develop a new Doppler lidar method for measuring winds with high accuracy and
high vertical resolution (20 m). The edge technique Doppler lidar method will be use to remotely measure atmospheric wind
profiles from ground-, air-, and space-based platforms. Remote wind measurements are important for meteorological and
climatological research at all spatial and temporal scales. Numerous studies have established the importance of global wind
measurements from satellites for improving weather forecasting skill. In addition, global wind measurements provide data that
are fundamental to the understanding and prediction of global climate change. A ground-based Doppler lidar system using the
edge technique has been developed at GSFC to obtain range-resolved measurements of atmospheric wind. Recently, the first
atmospheric wind measurements were obtained in the planetary boundary layer, the first 1-2 km of the atmosphere above the
surface. An example of the lidar profiles of wind speed and direction versus altitude is shown in Figure 15. The lidar values for
wind speed and direction are the average of twelve independent lidar profiles obtained in a 50-minute time period. The lidar
provides an independent wind measurement every 22 m in altitude. A rawinsonde balloon, launched simultaneously from a
nearby location, provided independent validation of the lidar measurements. The rawinsonde winds are also shown in the figure.
The lidar data are in good agreement with the rawinsonde data. The lidar instrument demonstrates a new capability which can
be used to obtain valuable information for studies of dynamics and turbulent processes in the lower atmosphere. This capability
could also be used for high-sensitivity detection of wind shear and microbursts in the vicinity of airports. Successful operation of
the lidar also supports the potential application of the edge technique as a space-based Doppler lidar wind sensor.
Cloud and Aerosol Lidar
Active lidar profiling of clouds and aerosols is an important adjunct to passive remote sensing of clouds. The ER-2
Cloud Lidar System (CLS) on the NASA ER-2 high-altitude aircraft has been an essential component of many cloud
measurement field studies. Field experiments include studies of the radiation properties of midlatitude and tropical cirrus clouds,
marine stratus clouds, arctic clouds and smoke clouds. The ER-2 lidar has participated in eight major field missions over the
last five years in diverse global locations. The lidar observations provide direct measurement of the cloud vertical structure.
These may be combined with passive measurements to both understand the three-dimensional structure of cloud radiative
forcing and determine the limitations of passive remote sensing. 
A dramatic example of Kelvin-Helmholtz waves observed by the CLS during the TOGA COARE field experiment in the tropical West Pacific is shown in
Figure 16. Important new technology for spaceborne lidar has been demonstrated by the ER-2 CLS instrument.
The instrument currently employs a highly advanced all solid-state laser and detectors.
Another cloud and aerosol lidar is the Visible and Near-IR Lidar (VIRL) which is an advanced, multi-wavelength, high-
sensitivity lidar instrument has been flown on the NASA DC-8 in field missions covering many regions around the globe. From
measurements by the DC-8 Lidar in several field missions, a detailed quantitative description of aerosol structure throughout the
Pacific basin region has been derived.
Micro Pulse Lidar
Micro Pulse Lidar (MPL) systems are state-of-the-art systems that are the first to be eye-safe, highly sensitive, and able
to be operated unattended. The technology was developed as an out growth of work on high-efficiency techniques for
spaceborne lidar. The first MPL system was designed and tested in the early 1990's at GSFC. MPL systems based on the prototype were installed at several Department of Energy Atmospheric Radiation Measurement (ARM) sites over the next several years. Several MPL systems have also been successfully deployed to major international field experiments aimed at cloud and aerosol studies. There are now many MPL systems in use around the world by researchers at various institutions, as well as our original MPL group at GSFC.
In order to fully exploit the unique characteristics of the MPL systems and the growing base of MPL users, a new NASA EOS funded project was begun by our group here at GSFC. The new project is the
Micro-pulse Lidar Network (MPL-Net).
MPL-Net began in May 2000, and is working to establish a worldwide network of MPL systems, all co-located with NASA's
AERONET
sunphotometer sites. MPL-Net will provide long-term monitoring of cloud and aerosol vertical profiles at key sites around the world. MPL-Net also provides support for field experiments using dedicated field systems. For more information on MPL systems and MPL-Net, visit the MPL-Net website.
|
|
| |
|
|
These water vapor data have been used to determine how advanced
statistical techniques (spectral, multifractal, and wavelet analysis) can be used to help understand the nature and causes of
atmospheric structure and variability. In addition to measuring water vapor, the Scanning Raman Lidar simultaneously measures
both aerosol backscattering and extinction. Figure 13 shows an example of simultaneous water vapor mixing ratio, relative
humidity, aerosol backscattering and extinction profiles. In addition to measuring aerosols in the lower troposphere, the lidar
system has also been used to measure profiles of the stratospheric aerosols produced by the June 1991 eruption of Mt.
Pinatubo. Temperature profiles in the upper troposphere and lower stratosphere are also derived from the lidar measurements.
Figure 14 (click to enlarge)is an image of laser backscatter from atmospheric aerosols and clouds from LASAL and LITE.
It extends from 24.43- N, 25.58- W to 13.01- N, 17.93- W off the west coast of north Africa. Levels of scattering are color
coded using black for low scattering, then going through blue, green, magenta, orange, and white for the highest scattering
levels. The planetary boundary layer (PBL) is the region of increased aerosol scattering indicated by red and white near the
ocean surface. Clouds are indicated by the regions of strong scattering at the top of the PBL (or at other altitudes) with a
vertical "shadow" below them. The broad area of aerosol scattering between 1.5 and 5 km altitude is a layer of Saharan dust,
lofted to these altitudes during the daytime, and advected over the ocean by the trade winds. Data such as these are used to
develop algorithms to derive boundary layer heights, lifting condensation level and entrainment zone thickness. In combination
with other remotely sensed data, water vapor and potential temperature profiles within the boundary layer can be derived.
These parameters help determine the latent and sensible heat flux between the ocean and the atmosphere.
A dramatic example of Kelvin-Helmholtz waves observed by the CLS during the TOGA COARE field experiment in the tropical West Pacific is shown in
Figure 16. Important new technology for spaceborne lidar has been demonstrated by the ER-2 CLS instrument.
The instrument currently employs a highly advanced all solid-state laser and detectors.
Another cloud and aerosol lidar is the Visible and Near-IR Lidar (VIRL) which is an advanced, multi-wavelength, high-
sensitivity lidar instrument has been flown on the NASA DC-8 in field missions covering many regions around the globe. From
measurements by the DC-8 Lidar in several field missions, a detailed quantitative description of aerosol structure throughout the
Pacific basin region has been derived.
In order to fully exploit the unique characteristics of the MPL systems and the growing base of MPL users, a new NASA EOS funded project was begun by our group here at GSFC. The new project is the
Micro-pulse Lidar Network (MPL-Net).
MPL-Net began in May 2000, and is working to establish a worldwide network of MPL systems, all co-located with NASA's
AERONET
sunphotometer sites. MPL-Net will provide long-term monitoring of cloud and aerosol vertical profiles at key sites around the world. MPL-Net also provides support for field experiments using dedicated field systems. For more information on MPL systems and MPL-Net, visit the MPL-Net website.