Space weather, the study of the Earth's upper atmosphere and forecasting its response due to solar events, depends on knowledge of the state parameters of the neutral and ionized upper atmosphere. In this work, we present a ground-based diode-seeded, high-power, narrow-linewidth Yb-fiber amplifier-based lidar operating at 1083 nm for measuring temperature and density of the neutral atmosphere from 300-1000 km. The current state of the lidar system will be addressed, as well as ongoing work to increase 1) signal to noise ratio through power scaling and 2) spatial resolution and wind measurement capability via pulsed operation.
Small satellites and payloads in the (1-2 kg) class called Cubesats and (20-30 kg) called Nanosats have been under
development at the University of Illinois since fall, 2001. The ION1 Cubesat was a 10x10x21.5 cm3 satellite with the
experiment consisting of photometric remote sensing of mesospheric structures (near 94 km) in the O2 (0,0) band
airglow at 762 nm. ION1 development began in 2001 and was lost on the failed launch attempt, July 26, 2006. ION2
development began in Fall 2005, and has a remote sensing experiment to measure Hα (656.3 nm) originating in the
Earth's geocorona from which column H densities can be deduced. Taylor University has led the development of a
Nanosat called TEST, which was designed to study ionospheric structures. Illinois provided remote sensing payloads
including a CCD camera and dual photometers. The development activity is largely implemented by a College of
Engineering Interdisciplinary Design class (ENG 491), where students typically participate in the systems engineering
experience for two semesters. The students (15-20 average enrollment) are responsible for the design, fabrication, and
testing of the systems. This paper describes the development of these Cubesat and Nanosat systems.
The direction, amplitude, and horizontal and vertical wavelengths are intrinsic attributes of Atmospheric Gravity Waves (AGWs) propagating through the upper atmosphere. The observable airglow modulation has been related to intrinsic amplitude through the 'cancellation factor', the horizontal wavelength from image measurements, the observed directions from image motion fields. The vertical wavelength is traditionally obtained using the wave dispersion relationship from the intrinsic phase speed, which is deduced from the observed phase speed in images and the Doppler correction from measured winds with either Na lidar or meteor radar. Methods of extracting vertical wavelength can also be deduced from measurements of phase shift with altitude through multiple airglows. Tomographic and multiple layer methods have been modeled and data has been analyzed to validate the methods. The multiple layer method enables the measurements to be made from ground-based imagers where winds are note available, or from spacecraft where phase speeds can't be measured.
Na Wind/Temperature lidar offers a method to study the dynamics and thermal structure of the mesosphere and lower thermosphere (MALT) through Doppler methods. The University of Illinois system has been operated at both the USAF Starfire Optical Range in Albuquerque, NM (94, 98-00') and at the USAF AMOS Maui facilities with receiving mirrors that are 3.5 m in diameter. An autonomous receiving system is being developed which will provide unrestricted and continuous operational capabilities. The bi-static operational receivers will be coupled with multiple fibers so that Na (589 nm) returns from the MALT region and Rayleigh (355 nm) returns from the stratosphere and mesosphere can be received simultaneously. The system will be described with attention to increased efficiencies in the receiver.
The University of Illinois Na wind/temperature lidar data collected at the Starfire Optical Range, New Mexico, can be used to present annual variations of the mesospheric mid-night horizontal winds. For each night, the winds profiles from the 11:00pm to 1:00am were smoothed in 1km altitude and then averaged in time to give mid-night winds profiles. All mid-night winds profiles within one month were averaged again to give mid night winds profiles of that month. The annual variations of the mid-night winds in the altitude ranges from 84km to 100km were obtained using a total of 46 nights lidar data distributed over the months except July. Zonal mid-night winds showed strong annual oscillations. Prevailing westerly winds blew over low altitudes in the winter months and over high altitudes in summer months. Meridional mid-night winds also showed annual or semi-annual oscillations. Southward winds dominated below 90km from April to October, and at about 96km during winter months and summer months except January. Correlations were found between the meridional mid-night winds and the mid-night temperatures. When the meridional winds blow from south, temperatures become warm. Results were compared with calculations of the HWM93 and the mid night winds observed with a MF radar at Urbana. Similar wind structures can be found in their results. The major differences are that strong westerly winds above 94km in March and April and strong northward winds at 96km in January were observed with the lidar. The winds values of the lidar and the MF radar data are larger than those of HWM93. Activities of inertial gravity waves and tidals might contaminated estimations of annual winds with the lidar data and contribute partially to their differences.
The University of Illinois Na wind/temperature lidar data collected at the Starfire Optical Range (SOR: 35N, 106.5W), NM, can be used to extract the dominant monochromatic inertial gravity waves and to characterize their features. By using simultaneously measured horizontal wind and temperature profiles the vertical wavelengths, intrinsic periods, and propagation directions can be determined using the hodograph method. A total of 700 waves were analyzed from about 300 h of observations. Waves with vertical wavelengths between 2 and 20 km and intrinsic periods between 1 and 20 h were fully characterized. 84.4% of the waves were propagating upwards. There was a prevailing direction towards the northeast in upward waves horizontal propagations over the year. This prevailing direction existed also in spring, summer and autumn. In winter, most waves propagated to the south and west. The filter theory of gravity waves propagating through the middle atmosphere can be used to give an explanation on the observations. Propagation directions of downward waves showed no prevailing directions over the year. A discussion was given on their different features for different seasons.
The Waves middle class Explorer mission (WE) is proposed to observe and quantify the effects of small-scale internal Gravity Waves (GW) in the Earth's atmosphere from source regions in the troposphere and lower stratosphere to the mesosphere, lower thermosphere, and ionosphere (MLTI) where the GW have their most dramatic effects. These are now understood to be a key element in defining large-scale circulation, thermal and constituent structures, and variability of the stratosphere and MLTI. The WE instrumentation consists of 5 nadir and limb viewing sensors of the wave perturbed emission structure due to GW throughout the source and affected regions. The WE PI is Prof. G.R. Swenson. This paper addresses the measurement strategy and implementation for two of these instruments, the Source Wave And Propagation Imager (SWAPI), and the Hydroxyl Airglow Wave Imager (HAWI). The SWAPI uses multi-spectral sublimb imaging measurements in the CO2 (nu) 3 band near 4210 nm to identify GW sources, and their propagation through the stratosphere. Its measurement strategy is driven by data, particularly sublimb images in the CO2 (nu) 3 band that were obtained by instrumentation deployed on the Midcourse Space Experiment (MSX) satellite, and by the WE team member's data analysis and models. Similarly team member's ground based observational experience and data analysis drives the HAWI measurement strategy.
Passive radiative cooling is desirable for space borne detectors because it is generally cheaper, less massive and power consumptive than cooling by a mechanical refrigerator or expendable cryogens. Our interest is space borne nadir imaging the OH airglow in Q-branch features of the 9->6 band at approximately 1382.3 nm, and the 2->0 band at approximately 1434.4 nm with sufficient signal to noise to quantitatively retrieve wave structure. Low noise 256 X 256- 40 micrometer pitch HgCdTe detector arrays are available for our application. E.g., the Rockwell Science Center standard 2.5 micrometers PACE product bonded on to the PICNIC read out MUL satisfies our high sensitive and low read noise requirements, but would require a mechanical refrigerator or expendable cryogen to cool sufficiently to satisfy our dark current requirement. To demonstrate an option that would provide our required performance at viable passive radiative cooling temperature, we have procured examples of the more recent RSC double layer planar heterogenous HgCdTe 2D arrays with shorter wavelength cutoff and produced by molecular beam epitaxy on a CdZnTe substrate, and bonded to the PICNIC MUL. Here we describe our test procedures and results that these at relatively warm temperature, the order 160 to 170K, satisfy the requirements for our OH airglow wave imaging application. We describe an instrument model and observational operations to observe the OH airglow wave structure with signal to noise > 100.
Airglow imaging instrumentation has been developed to provide quality imagery of airglow in the visible and near IR wavelengths. The lower thermosphere airglow layers emit between 85 and 102 km altitude. The layers are structured with nonuniformity in the horizontal dimension as a result of atmospheric gravity waves (AGWs) passing through the layer and disturbing the nominal recombination processes producing intensity and temperature modulations. Imagers have been developed to measure the AGW-produced airglow nonuniformities. The instrumentation combines large format, low noise CCDs with large aperture optics for improved S/N images. In particular, the large dynamic range of the detectors provides information from the low intensity zenith sky and the bright, van Rhijn enhanced horizon simultaneously in all-sky fields. The imagers have been used effectively to identify AGW structure from a number of ground based facilities as well as a recent NSF sponsored aircraft campaign. Imagery from the OH Meinel bands and OI 5577 angstrom are presented. Discussions are also presented regarding Na 5896 angstrom, and O2 atmospheric (0,1) band at 8650 angstrom emissions.
An imaging instrument is being developed for the NASA thermosphere ionosphere mesosphere energetics and dynamics (TIMED) mission. This instrument images the small, few km scale structure of the earth airglow. The measurement permits the remote sensing of the temperature and intensity fluctuations produced by atmospheric gravity waves propagating through the mesopause region. Instrument modules look in the nadir direction to observe the fine structure of the airglow. Other modules look at the limb in the satellite orbit plane to monitor the limb latitude profiles. The measurement is performed by observing the rotational temperature of the O2(0,0) band at 762 nm in nadir and limb. The waves also modulate the airglow intensity and the instrument will record the modulations of the O2(0,0), O2(0,1) and OH emissions in the nadir. The nadir channels of the instrument use a wide angle telecentric imager in which the distortion of the image is closely controlled so that the motion of the satellite can be compensated during the extended integration time by time delayed integration (TDI) mode of scanning of the CCD. The TDI method requires the CCD pixel columns to be aligned parallel with the orbital velocity vector and the shifting of the rows to be synchronized with the satellite motion. Through TDI scanning the imager can stare at a target at atmospheric altitude for an extended exposure duration. Each telecentric instrument module contains a single filter, and adjacent wavelength bands are imaged simultaneously by passing the light through the filter at different angles. The limb imagers use CCDs in the frame transfer mode.
A Loral 1024 X 1024 CCD array with 15-micron pixels has been incorporated as the focal plane detector in a new imaging spectrometer for auroral research. The large format low-noise CCD provides excellent dynamic range and signal to noise characteristics with image integration times on the order of 60 seconds using f/1.4 camera optics. Further signal enhancement is achieved through on-CCD pixel binning. In the nominal binned mode the instrument wavelength resolution varies from 15 to 30 angstrom across the 5000 to 8600 angstrom spectral range. Images are acquired and stored digitally on a Macintosh computer. This instrument was operated at a field site in Godhavn, Greenland during the past two winters (1993, 1994) to measure the altitude distribution of the various spectral emissions within auroral arcs. The height resolution on an auroral feature 300 km distant is approximately 1 km. Examples of these measurements are presented here in snapshot and summary image formats illustrating the wealth of quantitative information provided by this new imaging spectrometer.
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