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National Science Foundation Geospace Facilities Program

A Workshop to Develop a Large Aperture Lidar/Optical Facility for

Observations of the Upper Atmosphere from 30-1000 km

Chester S. Gardner, Principal Investigator University of Illinois

Gary R. Swenson, Co-Principal Investigator

University of Illinois

With

Patrick Espy, Collaborator Norwegian University of Science & Technology

Jeffrey Forbes, Collaborator

University of Colorado

David Hysell, Collaborator Cornell University

Hanli Liu, Collaborator

National Center for Atmospheric Research

John Plane, Collaborator University of Leeds

Markus Rapp, Collaborator

Leibniz Institute for Atmospheric Physics

Jeffrey Thayer, Collaborator University of Colorado

Richard Walterscheid, Collaborator

Aerospace Corporation

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Project Summary

We have organized a group of experts to help articulate the broad scientific rationale and develop the detailed design requirements for a major new lidar/optical facility to study the chemistry and dynamics of the Earth’s atmosphere from the middle stratosphere (~30 km) to well into the thermosphere (~1000 km). The objectives are to identify the key scientific problems currently challenging the middle and upper atmospheric sciences communities and determine what new observational capabilities, especially large aperture lidar systems, could facilitate significant progress in addressing those problems. It is envisioned that the centerpiece of the new lidar/optical facility would be a ~100 m2 collecting aperture that would consist of a 3-4 meter diameter fully steerable telescope in combination with a large array of smaller fix-pointed telescopes. In addition the facility would include important correlative instruments such as radars, imagers, spectrometers and perhaps in situ measurement capabilities using balloon and rocket probes. The specific project objectives are:

1. To determine the key scientific problems currently challenging the middle and upper atmosphere communities (with emphasis on those problems that could potentially benefit from the measurements achievable by a large aperture lidar/optical facility),

2. To determine what new observational capabilities could facilitate significant progress in addressing those problems,

3. To develop the top level design and operational requirements for the large optical telescope which would serve as the centerpiece of the new observatory,

4. To determine the design and operational requirements for the lidar systems that would utilize the large telescope,

5. To determine the key correlative instrumentation that would be essential to realize the full potential of the new observatory, and

6. To determine where the facility should be located to make the greatest contribution to science and to insure maximum operating productivity.

Intellectual Merit: The scientific motivation to explore the neutral properties of the middle atmosphere and thermosphere is compelling. The outstanding challenge in terrestrial upper atmosphere research is specifying the state of the space-atmosphere interaction region [CEDAR: The New Dimension, 2011]. There is growing recognition that meteorological sources of wave energy from the lower atmosphere are responsible for producing significant variability in the upper atmosphere. Furthermore, energetic particles and fields originating from the magnetosphere regularly alter the state of the ionosphere. These influences converge through tight coupling between the ionosphere plasma and neutral thermosphere gas to produce emergent behavior in the space-atmosphere interaction region (SAIR). Unfortunately measurements of the neutral thermosphere are woefully incomplete and in critical need to advance our understanding of and ability to model the SAIR. To fully explore neutral-ion coupling in the critical region above 100 km requires measurements of the neutral atmosphere to complement radar observations of the plasma. Lidar measurements of neutral thermospheric winds, temperatures and species can enable these explorations, an objective of highest priority for the upper atmosphere science community. The development of a large aperture, lidar/optical facility would do for thermosphere studies, much as incoherent scatter radar systems have done for ionosphere studies.

Broader Impacts: The proposed work has broader implications as it would provide a new opportunity for unique collaborations between the lower and upper atmosphere sciences communities, would develop state-of-the-art infrastructure for educating and training the next generation of researchers and would lead to direct observational studies and modeling of global climate change well into the thermosphere. It would also enable accurate measurements of atmospheric densities up to 1000 km that would substantially improve predictions of satellite (and debris) orbits in the important low-earth-orbit region.

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1. Introduction

The upper atmosphere [mesosphere, thermosphere and ionosphere] is a dynamic, complex region that interacts with its neighbors—the neutral gas-dominated lower atmosphere and the plasma-dominated space environment— through the transfer and transformation of energy, mass, and momentum…The outstanding challenge in terrestrial upper atmosphere research is specifying the state of the space-atmosphere interaction region (SAIR) at a particular time and location; a limitation manifest by significant levels of variability that often rival the value of the mean state. This variability is driven by the nonlinear, dynamical response of the SAIR to temporally and spatially changing fluxes of energy, mass, and momentum that cross its boundaries from space and the lower atmosphere...contemporary physics-based models of the upper atmosphere lack a complete set of inputs, boundary conditions, and validation procedures to adequately account for all relevant processes. A more complete understanding of the SAIR calls for more extensive spatial and temporal observations of multiple parameters simultaneously and more complete modeling development. [from CEDAR: The New Dimension, Strategic Vision for the NSF Program on Coupling, Energetics and Dynamics of Atmospheric Regions, May 2011]

We propose to organize a group of experts to help articulate the broad scientific rationale and develop the detailed design requirements for a major new lidar/optical facility to study the chemistry and dynamics of the Earth’s atmosphere from the middle stratosphere (~30 km) to well into the thermosphere (~1000 km). The scientific motivation to explore the neutral properties of the middle atmosphere and thermosphere is compelling. There is growing recognition that meteorological sources of wave energy from the lower atmosphere are responsible for producing significant variability in the upper atmosphere. Furthermore, energetic particles and fields originating from the magnetosphere regularly alter the state of the ionosphere. These influences converge through the tight coupling between the ionosphere plasma and neutral thermosphere gas to produce emergent behavior in the space-atmosphere interaction region (SAIR). Unfortunately measurements of the neutral thermosphere are woefully incomplete and in critical need to advance our understanding of and ability to predict the SAIR. To fully explore neutral-ion coupling in the critical region above 100 km requires measurements of the neutral atmosphere to complement radar observations of the plasma. Lidar measurements of neutral thermospheric winds, temperatures and species can enable these explorations, an objective of highest priority for the upper atmosphere science community. The development of a large aperture, upper atmosphere lidar/optical facility would do for thermosphere studies, much as incoherent scatter radar systems have done for ionosphere studies.

The development and refinement of sophisticated remote sensing technologies during the past five decades have contributed enormously to our knowledge of the atmosphere, especially the upper atmosphere above 30 km altitude. The availability and construction of major radar facilities, such as AMISR, Arecibo, EISCAT, Sondrestrom, Jicamarca, Millstone Hill and the MU Radar, have permitted researchers to study directly the ionized atmosphere with unprecedented accuracy and resolution while enabling inferences of neutral gas properties and dynamics. At the time these facilities were commissioned, each represented a major step forward in observational capabilities. Today these radars continue to play central roles in many ionospheric studies.

Lidar technology has enjoyed a similar renaissance since the invention of the laser 50 years ago. The first lidars were built in the 1930s and 1940s using mechanically modulated searchlights. Today, modern laser-based systems are used to probe composition and structure throughout the atmosphere from the troposphere into the lower thermosphere. The last two decades has been a period of substantial growth in lidar capabilities and applications, principally because of advances in critical areas of laser technology. Perhaps the most important of these has been the development of high-power, ultra-stable narrowband lasers, which are now being used in Doppler lidars for middle and upper atmosphere applications. Furthermore, robust tunable fiber lasers are also being used in laser guide star applications for ground-based astronomical imaging (http://www.gemini.edu/node/11603 ) and for sensing helium in the Earth’s thermosphere

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[Carlson et al., 2009]. Today space-borne systems such as IceSat (Ice, Cloud and Land Elevation Satellite, http://icesat.gsfc.nasa.gov/ ) and CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite, http://www-calipso.larc.nasa.gov/) are routinely providing global information on clouds and aerosols in the troposphere and stratosphere.

While the recent advances in lidar technology have been impressive, the accuracy, resolution, sensitivity and range of many systems are still limited by signal levels. Experiments conducted during the past fifteen years using the 3-meter class telescopes at the Starfire Optical Range, NM and Haleakala, Maui (Maui/MALT Program) demonstrated clearly the substantial scientific advantages of employing large steerable lidar telescopes in combination with correlative radars, passive optical instruments and rocket probes to study the middle and upper atmosphere. This project builds upon that prior work and recent laser technology advances by assembling a group of experts to articulate the scientific rationale and develop the design requirements for a major new facility to study the chemistry and dynamics of the Earth’s atmosphere from the middle stratosphere (~30 km) to well into the thermosphere using molecular and resonance fluorescence scattering to ~200 km and He resonance fluorescence scattering from ~200 to ~1000 km. This proposed capability would be a transformative step in understanding how a planetary atmosphere interacts with space. As will be shown in this proposal, there are no technology barriers to achieving this goal.

The centerpiece of the observatory would be a 10-meter class telescope that would serve as the receiving system for several very large lidar systems. By 10-meter class we mean a telescope with an effective aperture area comparable to a 10 meter diameter mirror (~100 m2). It is envisioned that the facility would consist of a large fully steerable telescope (3-4 meters in diameter) in combination with a large array of smaller fix-pointed telescopes (e.g. 10x10 array of 1 meter telescopes) yielding a total collecting area of approximately 100 square meters. The observatory would also include an appropriate complement of other important instruments such as radars, imagers, spectrometers and perhaps in situ measurement capabilities using balloon and rocket probes.

The large telescope collecting area in combination with modern high-power laser systems, would permit lidar measurements of winds, density, temperature and chemical composition with a sensitivity and resolution approximately 1000 times better than those which can be achieved with the most powerful systems in operation today. Depending on the application, it would be possible to develop instruments with power-aperture products of more than 104 Wm2 and permit researchers to study atmospheric processes with unprecedented accuracy and resolution. Such capabilities would enable the measurement of temperatures and winds up to 200 km altitude utilizing Rayleigh and metal lidar techniques and between about 200 and 1000 km utilizing a He resonance fluorescence lidar. These measurements would fill a critical knowledge gap in the thermosphere and enhance our understanding of electrodynamic effects that require knowledge of neutral winds and density. In addition, by employing Na, Fe and K metal lidar techniques, it would be possible to directly measure key turbulence processes and parameters like heat and constituent transport, eddy diffusivity and the turbulent Prandtl numbers below the turbopause (~110 km). Because the telescope would be designed specifically for lidar applications and be steerable, active experiments involving laser modification and chemical releases from satellites and rockets would open entirely new research areas.

2. Potential Measurement Capabilities of a 10-Meter Class Lidar Observatory

Although neutral thermospheric temperatures and winds have been routinely sampled in large spatial volumes from nightglow emissions at 630 nm, thermospheric structure including disturbances associated with waves, tides, and TIDs are only partially understood. Remote sensing measurements from limb viewing spacecraft have provided thermospheric temperature data, but temporally and spatially resolved measurements at sufficient resolution to study waves and tides are largely nonexistent. Fortunately, lidars with sufficiently large power-aperture products can fill this data gap. Since the invention of the laser in 1961, lidar systems have been developed to measure a wide variety of atmospheric constituents and parameters. To illustrate

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the greatly enhanced measurement capabilities that can be achieved with a very large optical observatory, we consider Rayleigh and metal lidar measurements of temperature in the lower thermosphere up to 200 km altitude and Doppler resonance fluorescence measurements of metastable He and temperatures between 200 and 1000 km.

2.1 Rayleigh Lidar

Elterman [1951; 1952; 1953] made the very first Rayleigh lidar measurements of stratospheric temperature and aerosol profiles sixty years ago using a bi-static configuration consisting of a zenith pointed searchlight and an off-axis vertically scanning telescope. For the more common mono-static configuration, the laser and receiving telescope are co-located. Range resolution is achieved by transmitting a pulsed laser beam and range gating the backscattered signal collected by the receiving telescope. The time of flight of the laser pulse corresponds to range.

Under appropriate conditions, the rms temperature error (!TRMS ) of a Rayleigh lidar is given by [Gardner, 2004]

!TRMS =T (z)SNR

. (1)

T(z) is the temperature at altitude z and the signal-to-noise power ratio (SNR) is

SNR = NR2 (z)

NR (z)+ NB

! NR (z) , (2)

where NR (z) is the Rayleigh signal count at altitude z and NB is the background noise count. When the laser beam and telescope are pointed vertically, the classic lidar equation for the Rayleigh signal count is given by

NR (z) =PLaser!hc / "

#(z)$ R!zATele

4% (z " zTele )2 &TeleTAtmos

2 (3)

where is the average power of the laser beam (W), is the integration period (s),

is the photon energy, , is

Planck’s constant, is the velocity of light, is the optical wavelength of the laser beam (frequency-doubled Nd:YAG laser), is the aperture area of the telescope (m2), zTele is the telescope alititude, is the optical efficiency of the telescope

including the quantum efficiency of the detector and is the 2-way optical transmittance of the atmosphere. The Rayleigh scattering probability is

(4)

where is the atmospheric density (m-3), is the Rayleigh backscatter cross-section (m2), is the vertical extent (resolution) of the observed scattering volume (m), is the

atmospheric pressure (mb) and is the atmospheric temperature (K).

PLaser !hc / ! = 3.74 •10"19 J ! / hc = 2.675 •1018 / J h = 6.63 •10!34 J / s

c = 3 •108m / s ! = 5.32 •10"7mATele

!Tele

TAtmos2

!(z)" R#z = 3.692 •10$31 P(z)T (z)

#z% 4.0117

= 5.458 •10$6 P(z)T (z)

#z

!(z) ! R

!z P(z)T (z)

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We now evaluate the measurement capabilities of one potential implementation of a mono-static Rayleigh lidar using the existing Gemini South 8 meter astronomical telescope at Cerro Pachon, Chile and a commercially available Nd:YAG laser. The key parameters of this facility are summarized in Table 1. The Coherent Mamba Green laser (Table 1) is diode laser pumped with a pulse rate of 10 kpps. To operate as a Rayleigh lidar to 200 km, the pulse rate must be reduced to 750 pps. This can be done without sacrificing power, by splitting the beam and using multiple fields-of-view. In Table 2 we summarize the SNR and measurement errors for a mono-static lidar operating during nighttime (when NB ! NR (z) ) that employs the Gemini South 8 meter telescope and a laser power of 325 W @ 750 pps. Scientifically useful atmospheric density and temperature measurements (better than ~10% accuracy) could be made to an altitude of 200 km.

Table 1. Cerro Pachon Observatory Parameter Cerro Pachon, Chile Location S 30o14.5’, W 70o44.1’ Altitude ( zTele ) 2.7 km

Telescope ( ATele ) Gemini South 8 m (50 m2)1

Optical Bandwidth (!" ) 0.2 nm Optical Efficiency (!Tele ) 0.5

2-Way Atmospheric Transmission (TAtmos2 ) 0.5

Laser Power (PLaser )2 325 W @ 10 kpps

Wavelength (! ) 532 nm Beam Divergence (!Laser ) 0.25 mrad

Power-Aperture Product (PLaserATele ) 16,335 Wm2 1Also available at Cerro Pachon, SOR 4 m (12.5 m2) telescope

2Coherent Mamba Green, High-Power, Q-Switched, Multimode Green Laser

Table 2. Gemini South 8-Meter Telescope - Cerro Pachon, Chile Δz = 5 km, Δλ=0.1 nm, PLaser=325 W @ 750 pps, θLaser=125 µrad

Altitude z

Model Temperature

T(z)1

Model Pressure

P(z)1

SNR=NR2/(NR+NB) ΔρRMS/ρ and ΔTRMS

τ=1 min τ=1 hr τ=1 min τ=1 hr

200 km 855 K 8.47•10-7 mb 76 11% 98 K 190 km 825 K 1.13•10-6 mb 175 7.6% 63K 180 km 790 K 1.53•10-6 mb 420 4.9% 39 K 170 km 748 K 2.12•10-6 mb 1.1•103 3.0% 23 K 160 km 696 K 3.04•10-6 mb 49 3.0•103 14% 99 K 1.8% 13 K 150 km 634 K 4.54•10-6 mb 146 8.8•103 8.3% 53 K 1.1% 6.8 K 140 km 560 K 7.20•10-6 mb 462 2.8•104 4.6% 26 K 0.6% 3.4 K 130 km 469 K 1.25•10-5 mb 1.6•103 9.4•104 2.5% 12 K 0.3% 1.5 K 120 km 360 K 2.54•10-5 mb 6.1•103 3.7•105 1.3% 4.6 K 0.2% 0.6 K 110 km 240 K 7.10•10-5 mb 3.4•104 2.0•106 0.5% 1.3 K 0.07% 0.2 K 100 km 195 K 3.20•10-4 mb 2.3•105 1.4•107 0.2% 0.4 K 0.03% 0.05 K

1U.S. Standard Atmosphere, 1976

2.2 Metal Lidars

Meteoric ablation is the source of metal atom layers in the mesosphere and lower thermosphere (MLT) above about 75 km altitude. Their existence was discovered by analyzing the spectra of atmospheric nightglow emissions [e.g. Slipher, 1929] and later confirmed by resonance fluorescence lidar measurements [e.g., Bowman et al., 1969]. During the past four

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decades lidar techniques have been developed to measure mesospheric Na, Fe, K, Ca, Ca+, and Li. Nowadays narrowband Fe, Na, and K lidars are used routinely to measure temperature and wind profiles in these metal layers, enabling detailed studies of the thermal structure, dynamics, and chemistry of the mesopause region (see summary by Chu and Papen [2005]).

The classic lidar equation for the resonance fluorescence signal count NS is similar to that for Rayleigh lidars

NS (z) =PLaser!hc / "

#S (z)$ eff (")!zATele

4% (z " zTele )2 &TeleTAtmos

2 , (5)

where !S (z) is the species concentration and ! eff (") is the effective resonance fluorescence backscatter cross section of the species. Under appropriate conditions, the rms temperature and radial wind errors (!TRMS !and !!VRMS ) for 3-frequency Doppler metal lidars are given by [Gardner, 2004]

!TRMS =1.8T (z)SNR

" 360KSNR

!VRMS =1.5 kBT (z) /mS

SNR" 250m / s

SNR

SNR = NS2 (z)

NS (z)+ NB

" NS (z)

, (6)

where T~200 K, kB =1.38x10!23J /K is Boltzmann’s constant and mS is the atomic mass of the

species. The larger the power-aperture product of the lidar (PLaserATele ), the larger the signal level NS and SNR and the smaller the measurement errors.

The advantages of employing large aperture telescopes to observe the metal layers are best illustrated by the data plotted in Figures 1 and 2. In Figure 1 are the temperature and Na density profiles through a persistent chemi-luminescent meteor trail that were measured during the 1998 Leonids meteor storm at the Starfire Optical Range, NM with a Na Doppler lidar (1.5 W) coupled to a 3.5 meter diameter astronomical telescope (~10 m2) [Chu et al., 2001]. Because of the large power aperture product (PLaserATele =14.4!Wm

2 ) and high Na densities within the meteor trail (up to 100 times higher than the background Na layer), it was possible to make accurate temperature and density measurements at high spatial and temporal resolutions (24 m and 15 s). The authors attributed the elevated temperatures at the edges of the Na-rich meteor trail to chemical heating.

Plotted in Figure 2 is the density of the background Na layer measured with an even larger broadband lidar [Pfrommer et al., 2009]. The laser power was 5 W and the telescope was a 6 meter diameter mercury mirror so thatPLaserATele =141!Wm

2 . The data are plotted at a resolution of 14.4 m and 60 ms. At this high resolution it is possible to observe Kelvin-Helmholtz instabilities and turbulence associated with breaking gravity waves. As these examples illustrate, the extremely large signal levels achievable with a 10-meter class telescope would permit Rayleigh, Na and Fe lidar measurements between 75 and 105 km altitude at resolutions and accuracies sufficient to study turbulence characteristics and directly measure the associated eddy diffusivities as well as the eddy heat and constituent transport [Gardner and Liu, 2010].

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Figure 1. Na density (dotted line, scale on the right) and temperature (solid line, scale on the left) profiles for the lower Diamond Ring meteor ablation trail observed at The Starfire Optical Range, NM (telescope diameter = 3.5 m) at 09:30:43 UT on 17 Nov 1998. The background temperature profile is plotted as the dashed line. The resolution is 24 m and 15 s. [from Chu et al., 2001].

Figure 2. Na density measured with the University of British Columbia Larger Zenith Telescope (diameter = 6 m) broadband Na lidar. The vertical resolution is 14.4 m and the temporal resolution is 60 ms [from Pfrommer et al., 2009].

Although the metal layers are primarily confined to the mesopause region between 75 and 105 km where they exhibit their highest densities, it is now known that tenuous layers of Na, Fe and K extend as high as 150 km [e.g. Hoffner and Friedman, 2004; Chu et al., 2011]. Recently Chu et al. [2011] reported observations of gravity wave signatures in Fe density and temperature profiles measured in the thermosphere up to 155 km at McMurdo, Antarctica with a modest Fe Boltzmann temperature lidar (PLaserATele = 0.5!Wm

2 ) (see Figure 3). This lidar consists of two independent channels probing the 372 and 374 nm absorption lines of neutral Fe atoms. Temperatures are inferred from the ratio of the signals in the two channels. While the metal densities at thermospheric heights are typically only a few tens to a few hundred atoms per cm3,

150

200

250

300

0

5 104

1 105

1.5 105

2 105

2.5 105

3 105

3.5 105

92 92.1 92.2 92.3 92.4 92.5T

empe

ratu

re (K

) Na D

ensity (cm-3)

Altitude (km)

09:30:43 UT 17 NOV 1998

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both temperature and wind profiles could be derived from lidar measurements made with a sufficiently large power aperture product instrument. In fact the collecting area of the large aperture, lidar/optical facility proposed here would be almost 800 times larger than the aperture used to obtain the McMurdo measurements illustrated in Figure 3. Utilizing such a large aperture would reduce the temperature errors in Figure 3 by a factor of 28. If, in addition to the telescope, the Boltzmann lidar was replaced by a 3-frequency Doppler Fe lidar of the same power, then the temperature errors in Figure 3 would be reduced by a factor of 50, yielding accuracies of ~8 K and ~5 m/s at altitudes as high as 150 km.

Figure 3. a) Fe density contour (cm-3) b) Fe density profiles at 372 and 374 nm and c) temperature (K) profile measured with an Fe Boltzmann lidar (telescope diameter = 0.4 m) at McMurdo, Antarctica on 28 May 2011. The vertical resolution is 2 km and the temporal resolution is 15 min [from Chu et al., 2011].

2.3 He Lidar

Almost fifteen years ago, it was proposed by Gerrard et al. (1997) that a naturally occurring metastable state of helium, He(23S), could act as an efficient scatterer in the Earth’s thermosphere at altitudes above approximately 200 km. With a powerful enough laser source operating at 1083 nm and a large receiving telescope, a He resonance fluorescence lidar system could be developed to probe the winds and temperatures associated with waves, tides and TIDs between 200 and 1000 km altitude, something that is of great interest to scientists studying the electrodynamics and plasma-neutral coupling of the Earth’s ionosphere-thermosphere system.

A bistatic He resonance fluorescence lidar is currently under development at the University of Illinois (G. R. Swenson’s group) for the purpose of measuring for the first time, thermosphere temperature and wind profiles above 200 km. The Illinois group has constructed

Event on May 28th, 2011 @ McMurdo

100 101 102 103 104 105707580859095

100105110115120125130135140145150155

Fe Density (cm 3)

Altit

ude

(km

)

(b) McMurdo 28 May 2011 @ 14.8 UT

372 nm Fe374 nm Fe

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and demonstrated the key element of the lidar, a diode-seeded, fiber amplified (10 W CW), narrow band (<1 MHz linewidth) laser, which is capable of being tuned to measure the Doppler broadened distribution of thermospheric He atoms in the (23S) metastable state, using resonant scattering at 1083 nm [Carlson et al., 2009]. The transmitter configuration consists of a master oscillator diode laser followed by a fiber power amplifier. A distributed Bragg reflector (DBR) grating laser diode operating at 1083 nm was developed at the University of Illinois (J. J. Coleman’s group) and is used for the master oscillator. The diode laser is frequency locked to the He(23S) transition using an absorption cell in which the He metastable state is generated with an RF discharge. Figure 4 is a photograph of the laser in the laboratory.

Figure 4. Photograph of the Ytterbium-doped fiber laser transmitter developed at the University of Illinois for the He(23S) resonance fluorescence lidar [Carlson et al., 2009].

The He(23S) lidar system is currently in test at the Urbana Atmospheric Observatory (UAO, 0.6 m2). The system will be deployed at Magdalena Ridge Observatory (MRO, 4.5 m2) near Socorro NM, in December 2011 for demonstration of first light. The expected SNR for the MRO installation is plotted in Figure 5. These calculations were made by assuming a twilight He(23S) population, a telescope diameter of 2.4 meters ( ATele =4.5 m2) and a laser power of 10 W with the lidar operating in the bi-static configuration. The detector is an Andor camera equipped with a deep depleted, high efficiency CCD array, cooled to -65C with a 3% QE. The combined optical efficiency of the transmitting and receiving optics is assumed to be 50%, the 1-way atmospheric transmittance is 50%, altitude resolution is 50 km and the integration period is 5 minutes.

Under appropriate conditions, the rms temperature error (!TRMS ) for a 3-frequency Doppler He lidar is given by [Gardner, 2004]

!TRMS =1.8T (z)SNR

. (7)

At 500 km where T~1000 K and the SNR reaches a maximum value of about 50 for the Magdalena Ridge Observatory installation (PLaserATele= 45 Wm2), the rms temperature error is expected be about 255 K. However, employing the Gemini South 8 meter telescope at Cerro

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Pachon, Chile (ATele=50 m2) and increasing the laser power to 100 W would raise the power-aperture product to 5000 Wm2 and increase the SNR given in Figure 5 by a factor of 111. Such a capability would directly enable high resolution sensing of temperature and wind profiles in the middle and upper thermosphere. For example, the SNR at 500 km would increase to 5,600 and temperature error would decrease to just 24 K. At 750 km the SNR would be ~2,500 and the temperature error would be 36 K. Even at 1000 km, the SNR would be a respectable 900 and the rms temperature error about 60 K.

Figure 5. Expected SNR for the He(23S) lidar at the Magdalena Ridge Observatory near Socorro, NM (telescope diameter = 2.4 m) where the power-aperture product is 45 Wm2.

These Rayleigh, metal and He lidar examples clearly illustrate the extraordinary measurement capabilities that could be achieved by using today’s laser technology in combination with a large optical telescope of a size comparable to existing astronomical facilities. Significantly, there are no technology barriers that would prevent making temperature and wind measurements of the neutral atmosphere well into the thermosphere to 1000 km. This capability would open an entirely new region of the Earth’s atmosphere to detailed studies of dynamics, chemistry and atmospheric modeling.

3. Project Objectives

We propose to organize a group of experts to help articulate the broad scientific rationale and develop the detailed design requirements for a major new lidar/optical facility to study the chemistry and dynamics of the Earth’s atmosphere from the middle stratosphere (~30 km) to well into the thermosphere (~1000 km). The objectives are to identify the key scientific problems currently challenging the middle and upper atmospheric sciences communities and determine what new observational capabilities, especially large aperture lidar systems, could facilitate significant progress in addressing those problems. It is envisioned that the centerpiece of the new lidar/optical facility would be a ~100 m2 collecting aperture that would consist of a 3-4 meter diameter fully steerable telescope in combination with a large array of smaller fix-pointed telescopes. In addition the facility would include important correlative instruments such as radars, imagers, spectrometers and perhaps in situ measurement capabilities using balloon and rocket probes.

The specific objectives are:

1. To determine the key scientific problems currently challenging the middle and upper atmosphere communities (with emphasis on those problems that could potentially benefit from the measurements achievable by a large aperture lidar/optical facility),

2. To determine what new observational capabilities could facilitate significant progress in addressing those problems,

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3. To develop the top level design and operational requirements for the large optical telescope that would serve as the centerpiece of the new observatory,

4. To determine the design and operational requirements for the lidar systems that would utilize the large optical telescope,

5. To determine the key correlative instrumentation that would be essential to realize the full potential of the new observatory, and

6. To determine where the facility should be located to make the greatest contribution to science and to insure maximum operating productivity.

4. Statement of Work

A 3-day Large Aperture, Upper Atmosphere Lidar/Optical Facility Workshop would be held in Chicago, IL during the spring 2012 to address all six of the objectives identified in Section 3. The Workshop would include both invited and contributed papers that address each objective. While the Workshop would be open to the whole atmospheric sciences community, attendance will be limited to ~30 participants. It will be important for certain key experts to participate. The PI and Co-PI, working in collaboration with the Workshop Steering Committee (see below), NSF program managers and the CEDAR Science Steering Committee, would identify key contributors who would be invited to participate and offered travel support to attend. It is envisioned that these invited contributors would broadly represent the atmospheric chemistry, dynamics, modeling and instrumentation communities.

A Workshop Steering Committee, co-chaired by PI Gardner and Co-PI Swenson and including other key scientists, would be formed and charged with the responsibility of organizing the scientific program of the Workshop and reporting its results. After the Workshop, the Steering Committee would prepare a detailed written report for NSF that thoroughly addresses all six of the project objectives. The Workshop Steering Committee members (all of whom have confirmed their willingness to serve) include:

• Chester Gardner (Co-chair), University of Illinois • Gary Swenson (Co-chair), University of Illinois • Patrick Espy, Norwegian University of Science & Technology

o Senior member of the atmospheric physics community, international leader on airglow studies of the chemistry and dynamics of the mesopause region

• Jeffrey Forbes, University of Colorado o Senior member of the atmospheric dynamics community, world’s leading

expert on atmospheric tidal modeling and on tidal interactions with the neutral and ionized atmospheres

• David Hysell, Cornell University o Senior member of the electro-dynamics community, international leader

in ionospheric electrodynamics and plasma instability studies • Hanli Liu, National Center for Atmospheric Research (NCAR)

o Senior member of the upper atmosphere modeling community, leads the thermosphere/ionosphere extension of the Whole Atmosphere Community Climate Model (WACCM)

• John Plane, University of Leeds o Senior member of the atmospheric chemistry community, acknowledged

world leader in global modeling of the meteoric metal layers • Markus Rapp, Leibniz Institute of Atmospheric Physics

o Senior member of the atmospheric physics community, expert on radar, lidar and sounding rocket probing of the upper atmosphere

• Jeffery Thayer, University of Colorado o Senior member of the CEDAR lidar community, immediate past chair of

the CEDAR Science Steering Committee, led the preparation of the strategic plan CEDAR: The New Dimension published in May 2011

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• Richard Walterscheid, The Aerospace Corporation o Senior member of the atmospheric dynamics community, developed key

theories describing the impact of waves on the structure and composition of the middle and upper atmospheres

This project benefits from and builds upon the considerable prior work of the CEDAR Science Steering Committee, who just released the 2011 CEDAR Stategic Plan (CEDAR The New Dimension, Strategic Vision for the NSF Program on Coupling, Energetics and Dynamics of Atmospheric Regions, May 2011), the CEDAR lidar community who prepared an extensive review of lidar accomplishments (CEDAR Lidar Beyond Phase III: Accomplishments, Requirement and Goals, March 2004) and an earlier report written by members of the research community on the scientific merits of large lidar systems (A Proposal for the Large Atmospheric Observatory, Draft Report, 16 October 1991).

The specific project activities are:

1. To form a Workshop Steering Committee, co-chared by the PI and Co-PI, that includes several other key scientists, for the purpose of organizing the Large Aperture, Upper Atmosphere Lidar/Optical Facility Workshop and reporting its results,

2. To organize and conduct the 3-day Workshop in Chicago, IL during spring 2012 and 3. To prepare a detailed written report for NSF that summarizes the outcomes of the

Workshop and addresses all six project objectives identified in Section 3.

5. Project Management and Timeline

This project is a collaborative effort involving researchers from the University of Illinois, Cornell University, National Center for Atmospheric Research, University of Leeds, Leibniz Institute of Atmospheric Physics, University of Colorado and The Aerospace Corporation. Professor Chester S. Gardner would serve as Principal Investigator and Professor Gary R. Swenson would serve as Co-Principal Investigator. In addition, Professors Jeffrey Forbes (U Colorado), Patrick Espy (Norwegian UST), David Hysell (Cornell), John Plane (U Leeds), Markus Rapp (Leibniz IAP), Jeffrey Thayer (U Colorado) and Dr. Richard Walterscheid (Aerospace Corp) would be key Collaborators.

PI Gardner would be responsible for overall project management and scientific guidance. He has considerable experience in successfully managing large complex scientific projects involving multiple investigators from different institutions (e.g. ALOHA-90, ALOHA-93, ANLC-93, LEONIDS-98, Maui/MALT). Co-PI Swenson is also an accomplished, highly respected scientist. He led the development of the novel 1083 nm fiber laser that is the key component of the He resonance fluorescence lidar. PI Gardner and Co-PI Swenson would be responsible for handling the local arrangements for the Workshop and organizing its scientific program. They would co-chair the Workshop Steering Committee and ultimately would be responsible for insuring that the project objectives are achieved and the final written report is submitted to NSF and disseminated to the broader scientific community.

Funds are requested to support the local costs of the Workshop (There would be no attendance fees.), which would be held at the University Club of Chicago, 76 East Monroe Street, Chicago, IL. Travel funds are requested to enable the Steering Committee Members and other key invited speakers to attend the Workshop and to enable the Steering Committee Members to interact while writing the final report following the Workshop.

Eighteen months of effort would be required to fully achieve the project goals. Funds are requested to support the project beginning 1 November 2011.

1 Nov 2011 – 30 Mar 2012: • Assemble the Workshop Steering Committee, • Organize and disseminate background materials to Workshop Steering Committee, • Organize the Workshop scientific program,

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• Invite key speakers and • Finalize the local arrangements for the Workshop.

1 Apr - 30 Jun 2012: • Conduct the Workshop • Process travel reimbursements • Disseminate Workshop materials to Steering Committee Members

1 Jul 2012 - 31 Dec 2012: • Prepare first draft of Workshop report with assistance of Workshop Steering

Committee and other key scientists 1 Jan 2013 - 28 Feb 2013:

• Disseminate draft report to key scientists for comment • Revise draft report and disseminate revision to NSF for comment

1 Mar 2013 – 30 Apr 2013: • Prepare final draft of Workshop report • Submit final report to NSF and disseminate to the CEDAR science community

6. Education Plan The primary product of this project is a detailed report in which the key middle and upper

atmosphere scientific problems are described and the potential for addressing those problems with the major instruments that would be associated with a large aperture, upper atmosphere lidar/optical facility are discussed. The report would serve current and future researchers and students by helping guide their research programs and instrument development. The PI and Co-PI will disseminate this report to the broader CEDAR and NSF communities to insure that scientists and students are aware of the potential contributions that optical remote sensing can make to middle and upper atmosphere science.

Most of the Collaborators (PI, Co-PI and Workshop Steering Committee Members) as well as most of the anticipated Workshop participants have faculty appointments at research universities. The synergy provided by this project would enhance on going research and education in their laboratories and contribute to their classroom teaching, especially at the graduate level in courses on optical remote sensing, aeronomy, atmospheric dynamics and atmospheric chemistry.

7. Data Management Plan

The primary product of this project is a detailed report in which the key middle and upper atmosphere scientific problems are described and the potential for addressing those problems with the major instruments that would be associated with a large aperture, upper atmosphere lidar/optical facility are discussed. The final report will be submitted to the NSF Geospace Facilities Program director for dissemination via the normal NSF channels, including the NSF website. Unrestricted access to the report will also be provided via the CEDARWiki and database maintained by the National Center for Atmospheric Research in Boulder, CO. ( http://cedarweb.hao.ucar.edu/wiki/index.php/Main_Page )

8. Intellectual Merit and Broader Impacts

The scientific motivation to explore the neutral properties of the middle atmosphere and thermosphere is compelling. The outstanding challenge in terrestrial upper atmosphere research is specifying the state of the space-atmosphere interaction region [CEDAR: The New Dimension, 2011]. There is growing recognition that meteorological sources of wave energy from the lower atmosphere are responsible for producing significant variability in the upper atmosphere. Furthermore, energetic particles and fields originating from the magnetosphere regularly alter the state of the ionosphere. These influences converge through tight coupling between the ionosphere plasma and neutral thermosphere gas to produce emergent behavior in the space-atmosphere interaction region (SAIR). Unfortunately measurements of the neutral thermosphere are woefully incomplete and in critical need to advance our understanding of and ability to model

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the SAIR. To fully explore neutral-ion coupling in the critical region above 100 km requires measurements of the neutral atmosphere to complement radar observations of the plasma. Lidar measurements of neutral thermospheric winds, temperatures and species can enable these explorations, an objective of highest priority for the upper atmosphere science community. The development of a large aperture, lidar/optical facility would do for thermosphere studies, much as incoherent scatter radar systems have done for ionosphere studies.

The proposed work has broader implications as it would provide a new opportunity for unique collaborations between the lower and upper atmosphere sciences communities, would develop state-of-the-art infrastructure for educating and training the next generation of researchers and would lead to direct observational studies and modeling of global climate change well into the thermosphere. It would also enable accurate measurements of atmospheric densities up to 1000 km that would substantially improve predictions of satellite (and debris) orbits in the important low-earth-orbit region.

9. References

Bowman, M. R., A. J. Gibson, and M. C. W. Sandford, “Atmospheric sodium measured by a tuned laser radar”, Nature, 221, 456–457 (1969)

Carlson, C. G., P. D. Dragic, R. K. Price, J. J. Coleman and G. R. Swenson, “A narrow linewidth Yb fiber-amplified-based upper atmospheric Doppler temperature lidar”, IEEE J. on Sel. Topics in Quantum Elec., 15(2), 451-461 (2009)

Chu, X., Z. Yu, C. S. Gardner, C. Chen, and W. Fong, “Lidar observations of neutral Fe layers and fast gravity waves in the thermosphere (110-155 km) at McMurdo (77.8oS, 166.7oE), Antarctica”, submitted to Geophys. Res. Letts., 22 Sep (2011)

Chu, X., and G. Papen, Resonance fluorescence lidar for measurements of the middle and upper atmosphere, in Laser Remote Sensing, edited by T. Fujii and T. Fukuchi, CRC Press, ISBN: 0-8247-4256-7, page 179-432 (2005)

Chu, X., A. Liu, G. C. Papen, C. S. Gardner, M. C. Kelley, J. Drummond, and R. Fugate, “Lidar observations of elevated temperatures in bright chemiluminescent meteor trails during the 1998 Leonid shower”, Geophys. Res. Letts., 27(13), 1815-1818 (2000)

Elterman, L. B., “The measurement of the stratospheric density distribution with the search light technique”, Journal of Geophysical Research, 56, 509-520 (1951)

Elterman, L. B., “A series of stratospheric temperature profiles obtained with the search light technique”, Journal of Geophysical Research, 58, 519-530 (1953)

Elterman, L. B., “Seasonal trends of temperature, density and pressure to 67.5 km obtained with the search light probing technique”, Journal of Geophysical Research, 59, 351-358 (1954)

Gardner, C. S., “Performance capabilities of middle-atmosphere lidars: comparison of Na, Fe, K, Ca, Ca+, and Rayleigh systems”, Applied Optics, 43, 4941-4956 (2004)

Gardner, C. S., and A. Z. Liu, “Wave-induced transport of atmospheric constituents and its effect on the mesospheric Na layer”, Journal of Geophysical Research, 115, D20302, doi:10.1029/2010JD014140 (2010)

Gerrard, A. J., T. J. Kane, D. D. Meisel, J. P. Thayer and R. B. Kerr, “Investigation of a resonance lidar for measurement of thermospheric metastable helium”, J. Atmos. Solar-Terr. Phys., 59(16), 2023-2035 (1997)

Hoffner, J. and J. S. Friedman, “The mesospheric metal layer topside: Examples of simultaneous metal observations”, J. Atmos. Solar-Terr. Phys., 67, 1226-1237 (2005)

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Slipher, V. M., “Emission in the spectrum of light in the night sky”, Publ. Astron. Soc. Pac., 41, 262-263 (1929)

Thayer, J. P., editor, “CEDAR: The New Dimension, Strategic Vision for the NSF Program on Coupling, Energetics and Dynamics of Atmospheric Regions”, 1-34 (2011)