ATMOSPHERIC REMOTE SENSING

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP91B00046R000100020015-3
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 21
• Document Creation Date: December 22, 2016
• Document Release Date: January 6, 2010
• Sequence Number: 15
• Publication Date: December 2, 1981
• Content Type: MEMO

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D?CTOR OF CENTRAL INTELLIG CE ~? ttAfv_o
Science and Technology Advisory Panel
0 2 DEC 1981
Executive Secretary , Science and
Technology- Advisory Panel
STAT
SUBJECT: Atmospheric Remote Sensing
1. As a follow-up to our discussions with JPL
personnel on atmospheric remote sensing, I would like you
to prepare a list of questions on the subject which I will
forward to JPL for answer. In the future, we may want to
follow-up these questions with a visit to JPL to discuss
them. In order to provide more background, and possibly
assist you in formulating your questions, I am forwarding
a list of JPL capabilities in remote sensing based upon
(1) existing instrumentation, (2) instrumentation under
development, and (3) analytical capabilities which have
arisen from current remote sensing of planetary atmospheres.
2. I have also attached a copy of E. David Hinkley's
recent article on advanced instrumentation for remote
sensing. Mr. Hinkley is the manager of JPL's Planetary
Atmospheres Section and Program Leader for Sensor Technology.
I anticipate that he will be in the Washington'. D.C. area
on 15-16 December. It may be possible to meet with him
again at that time.
3. I appreciate your participating in this effort
and request that you forward your questions to the STIC
Secretariat by Friday,l,i December for a consolidated request
to JPL.
STAT
Attachments:
A/S
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0
?
Dist.: STAT
Orig. - Addressees:
1 - STAP CHRONO
OSWR/STIC/STAP Dec 1981.
STAT
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FUTURE SPACE APPLICATIONS PAPER
E. D. Hinkley2
The need to measure meteorological and chemical properties of the Earth's
atmosphere on a global basis is becoming increasingly important, in view of
concerns about air quality, depletion of the ozone layer, and changes in the Earth's
radiation balance and weather patterns. Advanced techniques are now being
developed at several research centers which will enable key measurements to be
made which are now either impossible to make or in need of improvement. Remote
sensing from Spacelab/Shuttle and free-flying satellites will provide the platforms for
instrumentation based upon advanced technology. Several laser systems are being
developed for the measurement of tropospheric winds and pressure, and trace
species in the troposphere and stratosphere. With regard to other types of
instruments, a high-spectral-resolution, passive infrared sensor shows promise for
measuring temperature from sea level up through the stratosphere, and an advanced
microwave sounding unit is under consideration for the measurement of temperature
and moisture profiles as well as precipitation intensity for operational weather
forecasting. For wind measurements in the stratosphere and mesosphere, advanced
optical and microwave instruments are being developed. Microwave techniques are
also useful for measuring meteorological parameters at the air-sea interface. The
evolution and current status of such advanced instrumentation for future
measurements from space are described in this paper.
Several technologically-advanced instruments are being developed for global
measurements of the Earth's atmosphere from Shuttle and free-flying satellites. The
techniques involve transmission and/or detection of electromagnetic radiation, using
'The research described in this paper was carried out at the Jet Propulsion Laboratory,
California Institute of Technology, under contract with the National Aeronautics and Space
Administration.
'Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109.
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principles of absorption, emission, fluorescence, or scattering. The wavelength range
encompasses the microwave through the ultraviolet, and passive as well as active
instruments are being developed.
Several recent publications have gone into detail about the feasibility of using
advanced instruments for global measurements from space. Some of the more
general ones are the NASA Shuttle Atmospheric Lidar Research Program Report
[1], the NASA Upper Atmospheric Research Satellite Program Report [21, and the
report of the NASA Working Group on Tropospheric Pollution Planning [3]. Other
publications of a more specific and detailed nature will be cited below, especially
with regard to basic equations and signal-to-noise analyses which would require too
much space to be shown here.
This paper provides a survey of advanced instruments and techniques being
explored for global measurements of the Earth's atmosphere. Where possible,
comparisons are made with existing techniques, and estimates of the expected
measurement accuracy, spatial resolution, temporal resolution, and altitude of
optimum application will be given.
Principles of Remote Sensing
The basic physical principals on which most of the current remote sensing
instruments for species and meteorological measurements are based are
(1) absorption, (2) emission, (3) fluorescence, and (4) scattering [4]. Several of the
techniques to be described involve two of these mechanisms simultaneously. A brief
review of the basic principles is given in this section.
Absorption
Absorption of electromagnetic radiation by atoms or molecules serves as the basis
for remote measurements of several key species. Since nearly all molecules have rich
spectra in the infrared, between approximately 2 and 20 pin, and
pressure-broadening does not produce as severe a change in spectral signature as it
does at longer wavelengths, this region is generally recognized as being the most
useful one for species measurements based upon absorption. The Earth's atmosphere
itself also absorbs radiation (although the absorption is higher in the ultraviolet than
in the infrared), and this, together with some other considerations to be mentioned
below, make other wavelengths (e.g., microwave or ultraviolet) more attractive for
certain species.
Mathematically, for radiation of wavelength X, the presence of a molecular
species with a density N (cm-3) and optical cross-section a (cm2) at wavelength A,
the transmittance, T, of the radiation over a pathlength L (cm) is given by the
Beer-Lambert equation:
T = exp (-NaL).
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Equation (1) holds for narrow-band instruments, such as most lasers, which have
emitting bandwidths much narrower than the width of the spectral line being
interrogated. For other instruments, such as some spectrometers, Eq. (1) must be
modified, resulting in a smaller effective cross section, with concomitant loss in
sensitivity and specificity.
Instruments based upon the absorption of radiation through the atmosphere can
be either active (e.g., laser or microwave sources) or passive (e.g., spectrometers,
interferometers), and the detection process may involve either direct or heterodyne
techniques.
All atoms and molecules emit electromagnetic radiation when their temperature
is above absolute zero. Thus, the detection of this emitted radiation has been
incorporated into several passive spaceborne instruments and is being proposed for
several more. Measurements of meteorological parameters as well as species can be
made by detecting radiation emitted by the Earth's atmosphere.
Since passive heterodyne detection becomes more sensitive at longer wavelengths,
the sub millimeter and microwave regions are especially useful for detecting upper
atmosphere species where pressure broadening is low and background transmission
high. Detection of emissions lines in the infrared from certain minor species can also
serve as the basis for measurements of such meteorological parameters as
temperature and winds, based in the first case on a comparison of emission from
bands in different wavelength regions, and in the second case by subtle shifts in
emitted wavelength caused by the Doppler effect.
If radiation of an appropriately short wavelength (high energy) impinges upon
certain atoms and molecules, they can be made to fluoresce. Fluorescence
measurements are specific in two ways: (1) the wavelength of the incident
electromagnetic radiation must coincide with an absorbing wavelength of the
species; and (2) the fluorescent emission wavelength is characteristic of the species
as well. Laser radiation in the visible and ultraviolet regions of the spectrum has
been most useful in enabling the remote sensing of atoms and molecules using
fluorescence. Because fluorescence is quenched as background pressure increases,
and to avoid absorption by oxygen and other major components, the use of
fluorescence techniques to detect trace atoms and molecules is generally limited to
the upper atmosphere.
Scattering
Scattering of electromagnetic radiation by atmospheric constituents can be used
to provide information about the nature of the scatterers as well as the intervening
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atmosphere. Multiple-wavelength measurements of backscattering of laser radiation
from atmospheric aerosols in the ultraviolet through infrared regions of the
spectrum can provide information as to the concentration and size distribution of
the scattering centers, which are aerosol particles or molecules (depending on the
wavelength region used) in the atmosphere. Research is also proceeding toward the
development of techniques to remotely measure the chemical constituency of
aerosol particles as well.
Scattering from aerosol particles serves as the basis for Differential Absorption
Lidar (DIAL). These particles serve as scattering centers to reflect the laser radiation
back toward the receiver. For DIAL, the measurement technique is based on the
principle of absorption, discussed above, with time-gating of the return pulses used
to determine distance.
Global Meteorological Measurements
This section contains descriptions of "advanced instrumentation for remote
measurements of winds, temperature, and pressure from an orbiting spacecraft. The
discussion is arranged according to application, because in this context it is easier to
compare the measurement requirements with capabilities of existing instruments
and projected improvements expected from advanced instruments.
Global windspeed information is urgently needed in order to understand
transport and dynamics of the atmosphere, which bear strongly on the formation
and intensity of pollution episodes as well as on weather and climate, and of the
stratosphere and mesosphere in order to understand upper atmospheric dynamics.
Infrared Laser Instrumentation to Measure Tropospheric Winds. Although
cloud-tracking from orbiting satellites has been used in the past to indicate wind
fields, there are two factors which limit the usefulness of cloud-derived windspeed
information: (1) the altitudes of the clouds are unknown and do not cover all
regions of interest; (2) the relationship between cloud drifting rate and windspeed is
not well defined [5]. Even in the equatorial region, which is the main driver of
atmospheric dynamics, surface measurements are not made on a routine basis. There
is, therefore, a definite need for a new technique to measure tropospheric winds
from an orbiting spacecraft. The needed accuracy is 1-2 m/sec, with anywhere from
10 km to 400 km horizontal resolution, depending on whether the application is
operational forecasting or wide-scale modeling [6].
Huffaker has proposed [7] that a CO2-based infrared laser heterodyne system
could provide the necessary measurements of tropospheric winds from an orbiting
spacecraft-either Shuttle at an altitude of 250-300 km, or an operational satellite at
800 km altitude. An airborne. CO2 laser system using the same principle of
detecting the Doppler shift of back-scattered laser radiation has been operating at
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the Marshall Space Flight Center for several years [8] ; thus, the technique has been
demonstrated on a small scale. For particles with an average velocity component v
along the direction of the laser beam, the Doppler shift of the backscattered
radiation (scattered by aerosol particles moving with the wind field) is:
where vo is the original laser frequency and c the speed of light.
A spaceborne system to measure tropospheric winds would need a 10 joule CO2
laser operating at 20 Hz pulse repetition rate, with a frequency stability during each
pulse of 50 kHz or better [7, 9, 10]. The main difficulty seen for an operational
satellite is the large power requirement of the laser itself, of several kilowatts.
Although this power may be available on a 1-2 week Shuttle flight, it will require
advances in energy storage or production onboard the spacecraft, and improvements
in laser system efficiency, for flights of longer duration.
Measurements of Stratospheric Winds. The two techniques which show greatest
potential for measuring winds in the stratosphere are visible lidar and correlation
spectroscopy.
The visible lidar system is based upon backscattering from stratospheric
molecules and aerosol particles. The Doppler-induced frequency shift is detected
using a dispersive device, such as a Fabry-Perot etalon. It requires a very stable, pulsed
laser operating in the visible region of the specturm; this will be difficult to achieve.
A comprehensive article on the visible lidar approach to global wind measurements
was recently prepared by Abreu [11 ] .
A correlation-spectroscopy technique has been proposed [6], based upon
wind-induced Doppler shifts in thermal emission lines of gases present in the
atmosphere. Such measurements are made by viewing the limb of the atmosphere in
an infrared spectral interval which contains an emission band of a minor
constituent, such as N20, and optically correlating the emission lines with
absorption lines of the same gas contained in a cell within the instrument. It is this
correlation between the sets of spectral lines which constitutes a measurable
parameter related to the wind speed; for if there is relative motion between the
atmosphere and the gas in the cell, the atmospheric emission lines and the cell gas
absorption lines are no longer exactly superimposed due to the Doppler shift. This
approach to measuring stratospheric winds is now in the laboratory feasibility
demonstration phase.
Microwave Limb Sounder To Measure Mesospheric Winds. The Microwave Limb
Sounder (MLS) has been accepted for a Shuttle mission, with one of its goals to
measure upper atmospheric winds. The MLS measures both horizontal wind
components by means of an antenna system having two orthogonal fields of view. A
digital autocorrelator provides the spectral resolution required for observing winds
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by the Doppler shift in emission lines. In principle, the observed Doppler shift of
any microwave spectral line can be used, but the 118-GHz line of molecular oxygen
appears to provide the best signal-to-noise ratio to the highest altitudes [6]. Using a
10-sec integration time, the MLS is projected to provide windspeed information of
better than 10 m/sec in the altitude range of 70-110 km.
Wind Instrumentation Summary. It is obvious from the above discussions that no
single instrument can cover the entire altitude region of interest for global wind
measurements. Figure 1 illustrates this graphically, showing the main instruments
which have been described and their optimum regions of application.
Advanced Meteorological Temperature Sounder
During the past decade, numerical weather prediction models have evolved far
more rapidly than the capability of satellite-borne temperature sounders to supply
appropriate input data. The current generation of passive infrared sounders is
MLS
(t= 50 s)
VISIBLE LIDAR
1 10
NOISE-EQUIVALENT WIND (mis)
Instruments Except MLS, for Which it is 50 Sec
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CORRELATI ON
SPECTROMETERS
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capable of measuring tropospheric temperature with a vertical resolution of only 5-6
km, whereas 2 km or better is needed. This limitation in vertical resolution is
caused by the broadness of the weighting functions of current instruments. (When
the weighting functions are broad, the emitted energy reaching the satellite will have
components originating from a wide region of the atmosphere, thereby making
reconstruction of fine-scale vertical details practically impossible.) Because of this, as
well as cloud contamination and surface emissivity effects, the rms errors in the
retrieved temperature profiles of around 2.5 K are also above what is required by
the circulation models. The current generation of microwave sounding units for
temperature have a vertical resolution of 8 km in the troposphere, which is even
worse than the infrared. The microwave technique is better in the upper
atmosphere, however.
Design studies and numerical simulations have shown that an advanced
instrument can be developed which is capable of retrieving clear column
temperature profiles with a vertical resolution of 2 km in the troposphere and an
accuracy of 1.5 K even in the presence of multiple layers of broken clouds. This
new instrument is called the Advanced Meterological Temperature Sounder (AMTS),
and has been proposed by Chahine, Kaplan, and Susskind [12].
AMTS is an infrared sounder for which the desired temperature accuracy and
vertical resolution are achieved by careful choice of narrow-band channels in the
4.3-pm and 15-?m bands of CO2. For temperatures in the troposphere, this can be
met by a spectral resolution of 2 cm-' in the high-J lines of the R-branch; and in
the upper troposphere and stratosphere by a complementary set of 15-?m channels
with a spectral resolution of 0.5 cm-. Elimination of the effects of clouds is
accomplished by making simultaneous measurements in both bands.
A recent study [13] has shown that AMTS, with twenty-eight appropriately
selected infrared channels, will be able to make the following measurements from a
free-flyer spacecraft at an altitude of 800 km:
? Retrieve clear-column temperature profiles in the presence of up to three
layers of broken clouds with an average rms error of 1.5 K throughout most of
the troposphere;
? Simultaneously obtain humidity profiles with an accuracy of 20%;
? Recover day and night surface temperature of oceans and solid earth with an
average absolute accuracy of 1.5 K;
? Map the fractional cover and height of multiple cloud layers globally (as seen
from above) with a peak-to-peak accuracy of ?0.05 and 0.25 km, respectively;
? Determine the location of the tropopause to within 0.5 km_.
The Advanced Meteorological Temperature Sounder is being proposed for a
NASA free-flyer, Shuttle-launched mission in the mid-1980's. A CO2 laser technique
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has also been proposed to measure tropospheric temperature [14-16], but it is not
as far along as the AMTS in terms of readiness for an operational satellite.
Advanced Microwave Sounding Unit (AMSU)
for Temperature and Humidity
The AMSU is a 20-channel microwave radiometer system under consideration by
the National Aeronautics and Space Administration (NASA) and the National
Oceanic and Atmospheric Administration (NOAA) to provide soundings of
atmospheric temperature and humidity profiles and precipitation distributions for
operational weather forecasting. It utilizes rotational water vapor lines at 22.2 and
183.3 GHz for sounding the moisture profiles, and several channels in the 50-60
GHz oxygen band to sound the temperature profiles. The instrument is expected to
provide atmospheric temperature measurements with an average rms accuracy of
around 1.5 K between ground and 30 km altitude, and slightly less accurate profiles
to 50 km altitude. The humidity measurements will have an rms accuracy which is
better than or equal to the geometric sum of 0.2 g/cm2 and 10% of the measured
humidity.
The AMSU is the next generation microwave sounder for NOAA operational
applications and represents the fourth level of sophistication in NASA systems of
this type. Predecessor systems include the Nimbus 5 Microwave Spectrometer
(NEMS), Nimbus 6 Scanning Microwave Spectrometer (SCAMS) and the Microwave
Sounding Unit (MSU) currently being flown on TIROS-N and the subsequent NOAA
series spacecraft. The AMSU will be used aboard the Advanced TIROS-N (ATN)
spacecraft beginning with the NOAA-I mission.
Remote-Measurement Techniques
for Atmospheric Pressure
Global measurements of atmospheric pressure are important in synoptic
meteorology, numerical weather forecasting, atmospheric dynamics, and climate
studies. At the present time, pressure data are gathered principally from land-based
weather-monitoring stations, and are supplemented over the oceans by reports from
ships and aircraft. The lack of data over large areas of the globe (in particular, over
oceans in the southern hemisphere), poses a serious limitation for these studies.
The World Meteorological Organization has specified a set of observational'
requirements for the First Global Experiment of the Global Atmospheric Research
Programme [17]. Measurements of pressure in data sparse regions are required with
a horizontal resolution of 500 km and an accuracy of ?0.3%, equivalent to ?3 mb
at the surface. A recent survey of user needs [18] indicates that a slightly higher
accuracy of 1-2 mb may be desirable.
Microwave Pressure Sounder to Measure Surface Pressure. The Microwave
Pressure Sounder is an active instrument which emits bursts of energy in the
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60-GHz frequency region and detects the fraction backscattered from the sea
surface. The technique can provide surface pressure measurements over the ocean by
measuring beam absorption due to molecular oxygen, which is uniformly mixed
with other components of the atmosphere; the amount of oxygen being directly
proportional to atmospheric surface pressure. Other factors, such as the atmospheric
temperature profile, the presence of water vapor and liquid water, and the
properties of the ocean surface, also affect the measured absorption; however, the
microwave frequencies are selected to be in a region where these other absorptions
vary slowly with frequency, and their effects can be removed by making additional
measurements outside the oxygen band.
Spectroscopic calculations [19] show that the absorption coefficient for a
vertical path through the atmosphere varies as surface pressure raised to a power of
between 1.5 and 2 over the frequency range of interest. The nearer the frequency is
to the band center, the stronger will be the change in absorption coefficient for a
given change in surface pressure. A 6-channel instrument with an emitted power of
2 watts is expected to be able to measure surface pressure with a standard deviation
error of between 1 mb (no clouds) and 2 mb. In addition to, surface pressure, the
instrument will provide estimates of water vapor and liquid water content of the
atmosphere, and of the surface roughness of the sea. The Microwave Pressure
Sounder is being proposed as an instrument for a free-flying NASA satellite of the
mid-1980's.
Laser Measurements of Atmospheric Pressure. Because spectral lines broaden
with increasing background pressure, this phenomenon can be used as an indicator
of atmospheric pressure. Korb has proposed [15] to determine atmospheric pressure
on a global basis using a spaceborne laser system in which the transmittance is
measured of a laser beam whose wavelength is midway between two absorption lines
of molecular oxygen. By using the LIDAR (Laser Radar) technique, whereby only a
small region at a known distance from the spacecraft is probed, it should be
possible to derive the vertical profile of atmospheric pressure [20]. Laboratory
feasibility tests are currently underway to determine whether or not this laser
technique can measure pressure with the necessary precision.
Global Measurements of Atmospheric Species
Tropospheric Trace Species
Global measurements of several key tropospheric species can be made using
active laser techniques. Airborne measurements based on the principles of resonance
fluorescence [21] and differential absorption [22, 23] have shown potential for
future spaceborne applications.
The simplest laser approach to measuring tropospheric species is one based upon
differential absorption of continuous-wave (cw) laser radiation backscattered from
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the Earth's surface. Measurements of tropospheric ozone have been made over the
past few years from an airborne system using an instrument called the Laser
Absorption Spectrometer (LAS) [24]. Using two CO2 lasers, the LAS measures the
airplane-to-ground absorption due to ozone for a laser line which is absorbed by
ozone, and compares it with absorption of the second laser line which is beyond the
ozone-absorbing region. By ratioing the two return signals, effects of turbulence and
changing reflectivity of the Earth's surface are largely eliminated.
The present LAS system utilizes two 1-watt cw CO2 lasers, and has provided
ozone measurements on the west coast [251, east coast [26], and midwest [27].
Since range-gating is not possible with a cw system, no altitude-dependent studies of
species concentration can be made unless the airplane itself flies at different
altitudes. Some altitude information (with a vertical resolution of around 5 km) can
be obtained, however, using the pressure dependence of the spectral line shapes.
Extrapolations to Shuttle indicate that two 10-watt lasers will be able to perform
species measurements on a global basis. Species which may be measured with this
technique include 03, NH3, , C2 H4, CCQ4, C2 H3 CQ, and HNO3 .
A pulsed, tunable infrared laser can provide range information lacking with a cw
system, with the potential of providing 1 km vertical resolution. A laser with the
required wavelength coverage, energy (25 J/pulse), pulse repetition frequency (15
Hz), stability, and overall efficiency is not yet available, but laboratory development
is continuing.
Stratospheric Trace Species
The key question with regard to the stratosphere at the present time is, "Is the
ozone layer being depleted and thereby producing an increase in the amount of
solar ultraviolet radiation impinging on the Earth's surface?" A comprehensive
experimental and theoretical study sponsored by the U.S. Department of
Transportation looked at the ozone question in terms of emissions which would be
produced by a fleet of SST's (supersonic transports) [281. Using instruments that
were quite advanced at the time, and relying mainly on high-flying aircraft and
balloon flights, their conclusion was that there would be no discernible depletion of
stratospheric ozone arising from a fleet of SST's [29] . However, research is still
progressing in order to verify this finding and to study as well the potential impact
of sub-sonic commercial aircraft operating just below the stratosphere.
Whereas many of the species resulting from aircraft engine emissions and thought
to participate in ozone destruction are measurable with conventional techniques,
other reactions which may tend to deplete the ozone layer involve such
difficult-to-measure free radicals as CQO and HO2. Although some in situ techniques
do exist for these species, there are no remote-sensing techniques which would
permit their measurement from an orbiting spacecraft.
Trace species in the stratosphere have narrow infrared absorption lines, very near
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the Doppler limit of 0.002-0.01 cm-'. Conventional instruments, such as filter
channel infrared radiometers and spectrometers or interferometers have instrument
spectral widths which broaden the spectra, resulting in a potential loss in both
specificity and sensitivity. An advanced interferometer called ATMOS is being
constructed under a NASA contract to operate on Space Shuttle and provide a
rapid scan of the infrared "fingerprint" region, using solar occultation, of
stratospheric gases with a resolution of 0.01 cm-' . The Microwave Limb Sounder
(MLS) will provide species measurements in the upper stratosphere and mesosphere
from the Upper Atmospheric Research Satellite (UARS) when it is launched in the
mid 1980's.3
A laser heterodyne spectrometer (LHS) is a passive instrument which employs a
laser beam as local oscillator and a distant object, such as the sun, as the source of
radiation, with the measurement by solar occultation [30]. The JPL Laser
Heterodyne Radiometer (LHR), which is a specific instrument of the LHS variety,
has flown twice into the stratosphere to measure CQO. Good agreement was found
with in-situ measurements made by Anderson [31, 32].
Another laser heterodyne spectrometer is being constructed by NASA Langley
Research Center for operation onboard one of the Shuttle flights. It employs several
diode lasers as local oscillators, and will be able to measure a variety of atmospheric
trace species [33].
Table I is a summary of some of the atmospheric species for which laser
remote-sensing instrumentation is being developed. This is only a partial list because
of the wide variety of organizations throughout the world that are developing laser
instruments for their own specific applications.
'During the maiden flight of the balloon-borne MLS on 20 February 1981, the first
simultaneous remote measurements were made of 03 and CQO in the stratosphere. Results are
being analyzed and will subsequently be published [361.
Species
Region
H, 0
Atmosphere
Absorption; near-IR DIAL
Aircraft flights ongoing
OH
Atmosphere
Induced fluorescence
Aircraft flights ongoing
CO
Atmosphere
IR absorption
Aircraft flights ongoing
CH3 CQ
Atmosphere
Laser absorption spectroscopy
Spectroscopy in progress
03
Troposphere
IR absorption, DIAL
Aircraft flights ongoing
CQO
Stratosphere
Laser heterodyne spectroscopy
Balloon flights ongoing
HO2
Stratosphere
Laser heterodyne spectroscopy
Spectroscopy in progress
CQONO,
Stratosphere
Laser heterodyne spectroscopy
Spectroscopy in progress
NO,
Stratosphere
IR absorption
Balloon flight planned
03
Stratosphere
Induced fluorescence
Balloon flight planned
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Stratospheric Aerosols
Global measurements of aerosols in the stratosphere are needed primarily to
understand stratospheric heterogeneous reactions relating to the ozone depletion
question. In addition, stratospheric aerosols may affect our climate and, indirectly,
air quality. Clusters of sulfuric acid molecules (from sulfur compounds emitted at
ground level) are thought to act as condensation nuclei leading to the growth of
stratospheric aerosols which are the principal components of the Junge layer. The
sink for sulfur occurs when the heavier aerosols settle out of the stratosphere into
the troposphere, forming a dilute "acid rain." Consequently, in addition to measuring
the concentration and size distributions of aerosols in the stratosphere, it is
important to determine their chemical composition as well.
A High Spectral Resolution Lidar (HSRL) has been developed by researchers at
the University of Wisconsin [34] to measure the spatial distribution of the
atmospheric aerosol optical extinction coefficient on both regional and global scales.
The HSRL uses a nitrogen UV laser to optically pump a high spectral resolution dye
laser, the output of which is directed into the atmosphere. A 35-cm-diameter
receiver telescope collects the light backscattered by aerosol and air molecules, and
the return signal is analyzed using a high-spectral-resolution, two-channel
Fabry-Perot spectrometer.
The HSRL measures the aerosol optical extinction coefficient by distinguishing
light which is backscattered by the aerosol from that backscattered by air
molecules. Quantities such as the aerosol optical extinction coefficient,
backscattering phase function, aerosol-to-molecular scattering ratio, and visibility can
be derived from this information.
Identification of the chemical composition of stratospheric aerosol particles may
be possible using a multiwavelength (infrared) backscattering technique called DISC
[35]. A preliminary study of this approach indicates that sufficient lidar sensitivity
can be obtained at 220-km orbital altitude with 10-J CO2 laser and a 1-m-diameter
collector. The measurement principle is based on the fact that the aerosol particle
backscatter coefficient shows a dependence on wavelength that is characteristic of
its composition. This could also be a powerful tool for tropospheric aerosol analysis
if the backscatter signatures of different tropospheric aerosols are distinctive enough
for the technique to work.
Several key measurements of the Earth's atmosphere which must be made in
order for us to understand important processes relative to changes in the
stratospheric ozone concentration, in weather and climate, and in environmental
quality, cannot be made at the present time due to a lack of suitable
instrumentation. As a result of laboratory research into new detection techniques,
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Winds
Troposphere
Doppler/IR backscattering
CO2 lidar
Stratosphere
Doppler/VIS backscattering
VIS lidar
Correlation spectroscopy
IR correlator
Mesosphere
Doppler/emission
Microwave limb sounder
Temperature
IR emission
Advanced meteorological temperature sounder
Microwave emission
Advanced microwave sounding unit
Pressure
Sea-surface
Microwave absorption
Microwave pressure sounder
Troposphere
IR absorption
Laser pressure sounder
Species
Troposphere
IR absorption
Laser absorption spectrometer; IR DIAL
Stratosphere
Fluorescence
Laser fluorosensor
IR absorption
Laser heterodyne, ATMOS
Mesosphere
Microwave emission
Microwave limb sounder
Aerosols
< 0.5 gm dia
UV/VIS scattering
< 0.7 gm UV/VIS lidar
> 0.5 gm dia
IR scattering
> 0.7 pm IR lidar
advanced remote sensors are being developed with the expectation that several of
them will eventually be used to measure meteorological variables (winds, tempera-
ture, pressure) and species (trace molecules, atoms, and aerosol particles) on a global
basis. Some of the techniques described in this paper are listed in Table II along
with their potential applications. Many of these are expected to be deployed on
Shuttle or on free-flying operational spacecraft during the 1980's, and should
provide important inputs to our knowledge of the Earth's atmosphere.
Acknowledgment
The author would like to thank W. B. Grant, Ramesh Kakar, Harry Press, and
M. T. Chahine for their helpful comments, and Leticia Eckerle for typing the
manuscript.
Shuttle Atmospheric Lidar Research Program: Final Report of the Atmospheric Lidar
Working Group, NASA SP-433, November 1979.
Upper Atmosphere Research Satellite Program: Final Report of the Science Working
Group, JPL Publication 78-54, 15 July 1978.
NASA Tropospheric Program Plan: Working Group on Tropospheric Program Planning,
NASA Reference Publication 1062 (1981).
See, for example, Laser Monitoring of the Atmosphere, edited by E. D. Hinkley
(Springer-Verlag, Berlin, 1976).
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. is
[5] "Error Characteristics of Satellite-Derived Winds," L: Hubert and A. Thomasell, Jr.,
NOAA/NESS Publication, June 1979.
[6] Global Wind Workshop Summary Report, JPL Publication 715-15, 15 November 1979
(internal document).
[7] HUFFAKER, R. M. Feasibility Study of Satellite-Borne Lidar Global Wind Monitoring
System, NOAA TM ERL WPL-37, 1978.
[8] BILBRO, J. NASA Marshall Space Flight Center, private communication; see also, Ref. 6.
[9] "Aerosol Winds," Ref. 1, Experiment 20, pp. 144-146.
[10] HUFFAKER, R. M. "Feasibility of a Global Wind Measuring Satellite System
(WINDSAT)," Paper TuCI at the Topical Meeting on Coherent Laser Radar for
Atmospheric Sensing, 15-17 July 1980, Aspen, CO.
[11] ABREU, V. J. "Wind Measurements from an Orbital Platform using a Lidar System with
Incoherent Detection: An Analysis," Applied Optics 18, 2992 (1979).
[12] CHAHINE, M. T., KAPLAN, L. D., and SUSSKIND, J. "Advanced Meteorological
Temperature Sounder," unpublished, June 1979.
[13] CHAHINE, M. T. Jet Propulsion Laboratory, private communication, August 1980.
[14] MURRAY, E. R., POWELL, D. D., and VAN DER LAAN, J. E. "Measurement of
Atmospheric Temperature using a CO2 Laser Radar," Applied Optics 19, 1974 (1980).
[15] KALSHOVEN, J. E. and KORB, C. L. "Engineering a Laser Remote Sensor for
Atmospheric Pressure and Temperature," NASA TM-795381, 1978.
[16] "Temperature Profile," Ref. 1, Experiment 17, pp. 137-139.
[17] "The First GARP Global Experiment Objective and Plans," GARP Publication Series No.
11, World Meteorological Organization, Geneva, 1973.
[18] Follow-on Seasat User Needs Report, Report No. 624-1, Jet Propulsion Laboratory, 1976
(internal document).
[19] FLOWER, D. A. and PECKAM, G. E. A Microwave Pressure Sounder, JPL Publication
78-68, 1978.
[20] "Vertical Profiles of Atmospheric Pressure," Ref. 1, Experiment 16, pp. 134-136.
[21] BROWELL, E. NASA Langley Research Center, private communication.
[22] SHUMATE, M. S. and MENZIES, R. T. "The Airborne Laser Absorption Spectrometer: A
New Instrument for Remote Measurement of Atmospheric Trace Gases," Proc. 4th Joint
Conference on Sensing of Environmental Pollutants, New Orleans, 1978.
[23] WIESEMANN, W., BECK, R., ENGLISCH, W., and GURS, K. "In-Flight Test of a Continuous
Laser Remote Sensing System," Applied Physics 15, 257 (1978).
[24] MENZIES, R. T. and SHUMATE, M. S. "Tropospheric Ozone Distributions Measured with
an Airborne Laser Absorption Spectrometer," J. Geophysical Research 83, 4039 (1978).
[25] GRANT, W. B. and SHUMATE, M. S. Remote Measurements of Ozone Burdens in the
L. A. Basin on September 20 and 24, 1979 using the JPL Airborne Laser Absorption
Spectrometer, Final Report to the NASA Office of Technology Utilization, 1980.
[26] SHUMATE, M. S., MENZIES, R. T., GRANT, W. B., and MCDOUGAL, D. S. "Laser
Absorption Spectrometer: Remote Measurement of Tropospheric Ozone, Applied Optics
20, 525 (1981).
[271 SHUMATE, M. S. "Participation of the JPL Laser Absorption Spectrometer in the 1980
PEPE/NEROS Program in Columbus, Ohio," JPL Report 715-84, 28 July 1980 (internal
document).
[28] Proceedings, Fourth Conference, Climatic Impact Assessment Program, U.S. Department
of Transportation Report DOT-TSC-OST-7-38-1976.
[29] BRODERICK, A. "Stratospheric Effects from Aviation," AIAA/SAE 13th Propulsion
Conference, Orlando, FL, July 1977.
[30] MENZIES, R. T. "Atmospheric Monitoring using Heterodyne Detection Techniques,"
Optical Engineering 17, 44 (1978).
[31] MENZIES, R. T. "Remote Measurement of CQO in the Stratosphere," Geophysical
Research Letters 6, 151 (1979); R. T. Menzies, C. W. Rutledge, R. A. Zanteson, and D. L.
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Spears, "Balloon-Borne Laser Heterodyne Radiometer for Measurements of Stratospheric
Trace Species," Applied Optics 20, 536 (1981).
[32] ANDERSON, J. G., MARGITAN, J. J., and STEDMAN, D. H. "Atomic Chlorine and the
Chlorine Monoxide Radical in the Stratosphere: Three In-Situ Observations," Science 198,
501 (1977).
[33] ALLARIO, F. NASA Langley Research Center, private communication.
[34] SHIPLEY, S. T., ELORANTA, E. W., and TRACY, D. H. "Measurement of the Optical
Extinction Coefficient of Atmospheric Aerosols by Means of a High Spectral Resolution
Lidar," paper 2-10 presented at the 9th International Laser Radar Conference, Munich,
2-5 July 1979.
[35] WRIGHT, M. L., POLLOCK, J., and COLBURN, D. S. "DISC: A Technique for Remote
Analysis of Aerosols by Differential Scatter," 7th International Laser Radar Conference,
Menlo Park, CA, 4-7 November 1975.
[36] WATERS, J. W. Jet Propulsion Laboratory, private communication, March 1981.
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ATMOSPHERIC REMOTE SENSING CAPABILITIES
A. Using Existing Equipment with Minor Modifications
1. Laser Absorption Spectrometer for Active Remote Sensing and Measure-
ment of Gaseous Species in the Lower Atmosphere (Dr. M. S. Shumate :
Airborne and eventually spaceborne detection and measurement of
gaseous species. Has demonstrated usefulness by airborne measure-
ment over past several years over various area of the country.
2. High Resolution Ground-Based Interferometer for the Measurements of
Properties of the Atmosphere, Clouds, Dust, and Hazes (Dr. Reinhard
Beer): NASA-developed instrument, developed primarily for ground-
based astronomy, is available for atmospheric trace gas measurements
to infer both the properties of the sources of trace gases and char-
acteristics of the intervening atmosphere.
3. Detection and Communication using an Airborne Acousto-Optic Spec-
trometer (Dr. T. B. H. Kuiperl: An acousto-optic spectrometer) in-
tended to operate from an aircraft with a frequency resolution of
0.5 MHz over a bandwidth of 500 MHz, is being assembled. Continued
progress in solid state lasers and integrated optics devices are
expected to yield an instrument with unsurpassed frequency range,
stability, and sensitivity.
(4? Precise Position Determinations using Radio Interferometry (Dr. M.
Janssen): The Table Mountain radio interferometer and the Owens
Valley Radio Observatory millimeter interferometer represent avail-
able technologies for very precise determinations of position and
direction in passive and active systems.
5. Surveillance System for the Radio Frequency Region using the SETI
Multichannel Analyzer (Dr. S. Gulkis and Dr. E. Olsen ): An opera-
tional multichannel spectrum analyzer has been developed for the
RFISS and SETI programs. It will detect and measure 65,000 chan-
nels in the radio-frequency region with a bandpass of 20 MHz and a
resolution of 0.3 kHz.
6. Fast Near-Infrared Spectrometer for Remote Aircraft Surveillance
(Dr. J. Apt): The new JPL near-IR (0.6 - 5.4 microns) linear array
will detect and take spectra of objects 120 times faster than is
now possible. Its greatest military value would probably be in
high-speed airborne surveillance of the Earth's surface.
7. Field Measurements from Table Mountain Observatory (Dr. J. Apt):
The Table Mountain Observatory is well-situated both for communca-
tions with satellites, and the performance of photometry and spec-
tral measurements, as well as for operational tests of lasers and
other systems in cooperation with Edwards Air Force Base.
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8. Remote Sensing of Sea-Level Meteorology using SMMR (Dr. E. G.
Njoku : JPL has developed and demonstrated the use of an advanced
microwave instrument to remotely measure sea surface temperature,
winds, atmospheric water vapor, and liquid water content. The
instrument is the Scanning Multichannel Microwave Radiometer
(SMMR) which was flown on Seasat. Potential DoD applications
include ship routing, submarine detection, and surface and meteor-
ological data for directing field operations.
9. Microwave Instrumentation for Upper Atmosphere Measurements (Dr.
J. W. Waters): Microwave techniques for remote sensing of the
upper atmosphere (10-150 km) have been developed and partially
implemented. Experiments have been performed from ground, air-
craft, and balloon platforms, and are being developed for use on
spacecraft. By measurements of upper level winds, temperature,
magnetic field, and gaseous species, potential DoD applications
include trajectory determinations and improvement in theoretical
models for predicting atmospheric conditgions following nuclear
events such as 'forecasting communications capabilitiesd and fall-
out distribution.
B. Involving Development of New Instruments using Demonstrated Techniques
1. Infrared Spectroradiometer for Passive Remote Sensing and Meas-
urement of Gaseous Species in the Lower Atmosphere (Dr. Reinhard
Beer): Based upon instruments successfully implemented on the
Pioneer-Venus Spacecraft in 1978 and 1979.
2. Applications of Tunable Carbon Dioxide Lasers to Fieldable Systems
for Remote Species Detection (Dr. R. T. Menzies : Small, portable
carbon. dioxide laser systems for the remote detection of trace
gases in the atmosphere are now possible because of recent devel-
opments both at JPL and in industry. The spectral flexibility
offered by these lasers allows them to detect a wide variety of
gases in a battlefield environment.
3. Microwave Transmitter and Communication System (Dr. M. Janssen):
As a result of the development of a millimeter-wavelength horn
antenna with exceptionally high off-axis signal rejection, the
capabilitity exists for the construction of a system as a feed
for a secure microwave communication system or for a very high
efficiency radar transmitter.
4. All-Sky Wideband Maps using COBE (Dr. S. Gulkis): The development
of the COBE (Cosmic Background Explorer) instrument will permit
the complete mapping of the sky background diffuse infrared and
microwave radiation in the 1 micron to 13 millimeter wavelength
region.
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5. Large Space Telescope for Microwave Communication (Dr. T. Kuiper):
Preliminary designs have been made for a large 10-30 m far-in-
frared telescope based on active optics principles.
6. Spaceborne Optical Instrumentation (Dr. R. W. Carlson): JPL has
demonstrated capabilities in the area of spaceborne instrumenta-
tion for remote sensing, such as optical instrumentation, labora-
tory spectroscopy, and the ability to perform spectroscopic analy-
sis on remotely-sensed data.
7. Stratospheric Wind Measurements using Passive Infrared Sensing
(Dr. D. J. McCleese): The ability to measure stratospheric winds
with a passive infrared correlation sensor has been demonstrated
in the laboratory. Its potential application to military pro-
grams would be in the area of highflying aircraft, missiles, and
weather.
8. Remote Microwave Measurements of Meteorological Parameters (Dr.
D. A. Flower, Dr. R. K. Kakar, and Dr. E. G. Njoku): The Micro-
wave Sounder Unit (MSU) has been demonstrated on the TIROS-N
satellites. The Advanced Microwave Sounder Unit (AMSU), which
is an advanced version of the instruments already flown, will be
able to provide improved vertical resolution and coverage for
atmospheric temperature and moisture profiles and will provide
measurements of sea surface roughness as well. A Microwave
Pressure Sounder (MPS) is being developed for remotely atmos-
pheric surface pressure from satellites.
9. Microwave Technology and Systems Development (Dr. J. W. Waters):
As a result of a variety of field measurements using microwave
instrumentation over the past 20 years, JPL has developed an in-
house expertise to apply such instruments to a variety of applica-
tions. The ability to carry out such a project from design to
construction and field demonstration, without the need for sub-
stantial external inputs, represents a unique implementation
team.
C. Analytical Projects based on Space Research
1. Analytical Capability and Spectroscopic Information Bank Relevant
to Transmission of Electromagnetic Radiation, Radiative Transfer,
and Determination of Thermodynamic Parameters (Dr. Glenn S. Ort-
on):
The
capability
tion
and
radiative
for
other
planetary
military
needs.
exists at JPL to analyze atmospheric propoga-
properties, based upon technology developed
atmospheres, which are of direct interest to
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2. Non-LTE Radiative Transfer Theory (Dr. J. Appleby): Radiative
transfer methods have been developed to treat the breakdown of
local thermodynamic equilibrium (LTE), which occurs in the up-
per layers of all planetary atmospheres. Terrestrial applica-
tions include analyses of emissions from exhaust plumes, and
laser beam transmission.
3. Analysis of Remote Sensing Data (Dr. R. W. Carlson): Studies of
the atmospheres and surfaces of other planets have necessitated
the development of a capability to accurately assess the signifi-
cance of the data received. This capability can be applied di-
rectly to DoD Earth-observing missions in such areas as meteorol-
ogy, gaseous transport and chemical conversion, and various indi-
cators of surface changes in vegitation and vehicular transport.
4. Speckle Imaging to Reduce Amospheric Blurring (Dr. J. Apt): JPL
has developed an ability to achieve spatial resolution approxi-
mately five times greater than is permitted by atmospheric blur-
ring. This could be valuable for improving the resolving power
of long-range photography.
5. Image Processing and Large Data Base Manipulation (Dr. L. S.
Elson): The ability to perform advanced image and large data base
processing would have military applications in terms of under-
standing thermal balance of the atmosphere, albedo, upper atmos-
pheric waves, circulation and transport, and cloud structure and
morphology.
6. Electromagnetic Wave Propagation Predictions (Dr. H. M. Pickett):
Computer models for predicting electromagnetic wave propagation
in the 0-3000 GHz region have been developed and extensively
tested at JPL for altitudes to 150 km. A catalogue of atmospheric
spectral lines and parameters for frequencies up to 3000 GHz has
been assembled and is continuously being upgraded. Potential
DoD applications include prediction of propagation characteristics
under a variety of field operational scenarios, and developing
secure communications sytems.
7. Communication in the Presence of Irregular Particles (Dr. M. S.
Hanner): Scattering from irregularly-shaped particles can have a
noticeable effect on communications. In depth studies of the re-
flection and scattering of electromagnetic radiation from such
particles have been made in order to examine the properties of
interstellar dust clouds and cometary tails. The influence of
such dust particles on communication through the atmosphere can
be ascertained by applying this analytical procedure in reverse.
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