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The accuracy and precision of the Upper Atmosphere Research Satellite (UARS) Microwave Limb Sounder (MLS) atmospheric temperature and tangent-point pressure measurements are described. Temperatures and tangent-point pressure are retrieved from a 15-channel 63-GHz radiometer measuring O 2 microwave emissions from the stratosphere and mesosphere.
The accuracy and precision of the Upper Atmosphere Research Satellite (UARS) Microwave Limb Sounder (MLS) atmospheric temperature and tangent-point pressure measurements are described. Temperatures and tangent- point pressure (atmospheric pressure at the tangent height of the field of view boresight) are retrieved from a 15-channel 63-GHz radiometer measuring O2 microwave emissions from the stratosphere and mesosphere. The Version 3 data (first public release) contains scientifically useful temperatures from 22 to 0.46 hPa. Accuracy estimates are based on instrument performance, spectroscopic uncertainty and retrieval numerics, and range from 2.1 K at 22 hPa to 4.8 K at 0.46 hPa for temperature and from 200 m (equivalent log pressure) at 10 hPa to 300 m at 0.1 hPa. Temperature accuracy is limited mainly by uncertainty in instrument characterization, and tangent-point pressure accuracy is limited mainly by the accuracy of spectroscopic parameters. Precisions are around 1 K and 100 m. Comparisons are presented among temperatures from MLS, the National Meteorological Center (NMC) stratospheric analysis and lidar stations at Table Mountain, California, Observatory of Haute Provence (OHP), France, and Goddard Spaceflight Center, Maryland. MLS temperatures tend to be 1-2 K lower than NMC and lidar, but MLS is often 5 - 10 K lower than NMC in the winter at high latitudes, especially within the northern hemisphere vortex. Winter MLS and OHP (44 deg N) lidar temperatures generally agree and tend to be lower than NMC. Problems with Version 3 MLS temperatures and tangent-point pressures are identified, but the high precision of MLS radiances will allow improvements with better algorithms planned for the future.
The Microwave Limb Sounder (MLlS) experiments obtain measurements of atmospheric composition, temperature and pressure by observations of millimeter and submillimeter-wavelength thermal emission as the instrument field-of-view is scanned through the atmospheric limb.
The Scanning Microwave Limb Sounder (SMLS) is a space-borne heterodyne radiometer which will measure pressure, temperature and atmospheric constituents from thermal emission between 180 and 680 GHz. SMLS, planned for the Global Atmospheric Composition Mission of the NRC Decadal Survey, uses a novel toric Cassegrain antenna to perform both elevation and azimuth scanning. These provide better horizontal and temporal resolution and coverage than were possible with elevation-only scanning at typical Low-Earth orbit spacing in the two previous MLS satellite instruments. Development of the SMLS antenna was the focus of a 2006 Small Business Innovative Research (SBIR) program whose phase II culminated in the fabrication and thermal stability testing of a composite demonstration model of the SMLS primary reflector. This reflector has the full 4m height and 1/3 the width planned for flight. An Instrument Incubator Program (IIP) titled "A deployable 4 Meter 180 to 680 GHz antenna for the Scanning Microwave Limb Sounder" continues development of the SMLS antenna with the study of 5 topics: 1) detailed mathematical modeling of the antenna patterns from which we simulate geophysical parameter retrievals in order to establish FOV performance requirements; 2) thorough correlation of finite element model predictions with measurements made on the SBIR reflector. We will again measure deformations of this reflector, under more flight-like thermal gradients, using higher precision metrology techniques available in a new large-aperture facility at JPL; 3) fabrication of a full-width primary reflector whose asbuilt surface figure will better meet the figure requirements of SMLS than did the SBIR reflector; 4) integration of the primary with other reflectors, and with residual front ends built in a 2007 IIP, in a breadboard antenna; and finally 5) RF testing of the breadboard on a Near Field Range at JPL. We report on significant progress in 3 areas of the current IIP: development of the mathematical model to predict SMLS antenna patterns and their application in a preliminary set of geophysical retrievals; the correlation between surface deformation predicted by finite element models and measurement in the 2009 isothermal stability tests of the SBIR, with implications for the thermal gradient testing to be performed at JPL; and aspects of the conceptual design of the full-width primary reflector to be fabricated and tested in the 2nd and 3rd years of the IIP.
The Scanning Microwave Limb Sounder (SMLS) is a space-borne heterodyne radiometer which will measure pressure, temperature and atmospheric constituents from thermal emission in [180,680] GHz. SMLS, planned for the NRC Decadal Survey's Global Atmospheric Composition Mission, uses a novel toric Cassegrain antenna to perform both elevation and azimuth scanning. This provides better horizontal and temporal resolution and coverage than were possible with elevation-only scanning in the two previous MLS satellite instruments. SMLS is diffraction-limited in the vertical plane but highly astigmatic in the horizontal (beam aspect ratio approx. 1:20). Nadir symmetry ensures that beam shape is nearly invariant over plus or minus 65 deg azimuth. A low-noise receiver FOV is swept over the reflector system by a small azimuth-scanning mirror. We describe the fabrication and thermal-stability test of a composite demonstration primary reflector, having full 4m height and 1/3 the width planned for flight. Using finite-element models of reflectors and structure, we evaluate thermal deformations and optical performance for 4 orbital environments and isothermal soak. We compare deformations with photogrammetric measurements made during soak tests in a chamber. The test temperature range exceeds predicted orbital ranges by large factors, implying in-orbit thermal stability of 0.21 micron rms (root mean square)/C, which meets SMLS requirements.
The scanning microwave limb sounder (SMLS) is the latest instrument to probe the Earth's atmosphere to come out of the Microwave Limb Sounder (MLS) team. Once deployed to the upper stratosphere, it will use microwave detection to measure geo-atmospheric variables such as temperature, pressure, and chemical composition. In addition to previous missions that used vertical limb scans to observe altitudinal variations, the SMLS will rotate laterally allowing it to establish two-dimensional variable dependencies with a single run. A program was originated by a previous intern that will automatically control the movement of the two rotational axes along with a switching mirror and chopper once the instrument is in flight. However, it lacked the code essential to control system's ability to function fully and reliably. By modifying and rewriting parts of the code I sought to have a finished ready-for-flight control system that would be easy to navigate. Three of the major alterations I made including instituting a gyroscope, implementing a restart button, and instigating the automatic creation of a file log with each run to record the position and orientation of the SMLS.
The Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite (UARS) has provided measurements of O(sub 3), H(sub 2)O, CIO, SO(sub 2), HNO(sub 3), temperature and pressure in Earth's atmosphere. These measurements are made near-globally both dat and night and are not degraded by the presence of aerosols, cirrus or polar sratospheric clouds.
Development of a high accuracy spherical microwave reflector to support contour RMS and pointing requirements for a new series of space instruments is reported. The reflector system is composed of precision machined aluminum tile reflectors supported from a eutectic coated graphite epoxy structure by flexures. Several basic technologies have been integrated into a manufacturing process that accommodates fabrication techniques of both optical and composite constraints. The optical figure and its change due to thermal gradient was measured in a thermal vacuum environment with a Ronchi system. The radiometer system is in support of the Microwave Limb Sounder, an experiment to measure emissions from earth's atmospheric limb thus obtaining wind, temperature, pressure and chemical composition measurements.
An advanced Microwave Limb Sounder (MLS), now in concept development for a potential future mission, is a space-borne heterodyne instrument to measure pressure, temperature, and atmospheric constituents from thermal emission between 120 and 2400 GHz. Previous MLS instruments used pencil-beam antennas sized to resolve N 1 vertical scale height. Current atmospheric models need better horizontal resolution than orbit spacing provides. To meet these needs, a new antenna concept combines the wide scan range of the parabolic torus with unblocked offset Cassegrain optics. The resulting system is diffraction-limited in the vertical plane but extremely astigmatic, with beamwidths 0.13~2.5. Nadir axis symmetry ensures that this Beam AspectRatio (BAR) is invariant over f33' of azimuth. The antenna can feed either an array of receivers or multiplexed low-noise receivers whose FOVs are swept by a small scanning mirror. We describe 3 stages of antenna design: First, using a paraxial-optics method, we choose conic profiles given vertical resolution orbit geometry, then develop the surfaces by nadir axis rotation, matching axisymmetric feeds to the BAR. A ray-trace program validates the design and generates alignment and deformation tolerances. Finally, a physical optics analysis verifies reflector surface currents and radiation patterns.
The Microwave Limb Sounder instrument was launched aboard NASA's EOS AURA satellite in July, 2004. The overall scientific objectives for MLS are to measure temperature, pressure, and several important chemical species in the upper troposphere and stratosphere relevant to ozone processes and climate change. MLS consists of a suite of radiometers designed to operate from 11 8 GHz to 2.5 THz, with two antennas (one for 2.5 THz, the other for the lower frequencies) that scan vertically through the atmospheric limb, and spectrometers with spectral resolution of 6 MHz at spectral line centers. This paper describes the on-orbit commissioning the MLS instrument which includes activation and engineering functional verifications and calibrations.
We describe the fabrication and thermal-stability analysis and test of a composite demonstration model of the Scanning Microwave Limb Sounder (SMLS) primary reflector, having full 4m height and 1/3 the width planned for flight. SMLS is a space-borne heterodyne radiometer which will measure pressure, temperature and atmospheric constituents from thermal emission between 180 and 660 GHz. Current MLS instruments in low Earth orbit scan pencil-beam antennas (sized to resolve about one scale height) vertically over the atmospheric limb. SMLS, planned for the Global Atmospheric Composition Mission of the NRC Decadal Survey, adds azimuthal scanning for better horizontal and temporal resolution and coverage than typical orbit spacing provides. SMLS combines the wide scan range of the parabolic torus with unblocked offset Cassegrain optics. The resulting system is diffraction-limited in the vertical plane but highly astigmatic in the horizontal, having a beam aspect ratio [tilde operator]1:20. Symmetry about the nadir axis ensures that beam shape is nearly invariant over +/-65(white bullet) azimuth. The a feeds a low-noise SIS receiver whose FOV is swept over the reflector system by a small scanning mirror. Using finiteelement models of antenna reflectors and structure, we evaluate thermal deformations and the resulting optical performance for 4 orbital environments and isothermal soak. We compare deformations with photogrammetric measurements made during wide-range (ambient+[-97,+75](white bullet) C) thermal soak tests of the primary in a chamber. This range exceeds predicted orbital soak ranges by large factors, implying in-orbit thermal stability of 0.21(mu)m rms/(white bullet)C, which meets SMLS requirements.
The microwave limb sounder (MLS) on the Upper Atmosphere Research Satellite (UARS) is the first satellite experiment using limb sounding techniques at microwave frequencies. Primary measurement objectives are stratospheric ClO, O3, H2O, temperature, and pressure. Measurements are of thermal emission: all are performed simultaneously and continuously and are not degraded by ice clouds or volcanic aerosols. The instrument has a 1.6-m mechanically scanning antenna system and contains heterodyne radiometers in spectral bands centred near 63, 183, and 205 GHz. The radiometers operate at ambient temperature and use Schottky-diode mixers with local oscillators derived from phase-locked Gunn oscillators. Frequency tripling by varactor multipliers generates the 183- and 205-GHz local oscillators, and quasi-optical techniques inject these into the mixers. Six 15-channel filter banks spectrally resolve stratospheric thermal emission lines and produce an output spectrum every 2 s. Thermal stability is sufficient for 'total power' measurements which do not require fast chopping. Radiometric calibration, consisting of measurements of cold space and an internal target, is performed every 65-s limb scan. Instrument in-orbit performance has been excellent, and all objectives are being met.
The Observatoire de Haute Provence (OHP) weekly Electrochemical Concentration Cell (ECC) ozonesonde data have been homogenized for the period 1991-2021 according to the recommendations of the Ozonesonde Data Quality Assessment (O3S-DQA) panel. The assessment of the ECC homogenization benefit has been carried out using comparisons with other ozone measuring ground based instruments at the same station (lidar, surface measurements) and with collocated satellite observations of the O3vertical profile by Microwave Limb Sounder (MLS). The major differences between uncorrected and5homogenized ECC data are related to a change of ozonesonde type in 1997, removal of the pressure dependency of the ECC background current and correction of internal pump temperature. The original 3-4 ppbv positive bias between ECC and Lidar in the troposphere is corrected with the homogenization. The ECC 30-years trends of the seasonally adjusted ozone concentrations are also significantly improved in both the troposphere and the stratosphere after the ECC homogenization, as shown by the ECC/lidar or ECC/surface ozone trend comparisons. A -0.19% per year negative trend of the normalization factor (NT)10calculated using independent measurements of the total ozone column (TOC) at OHP disappears after homogenization of the ECC data. There is however a remaining -3.7% negative bias in the TOC which is likely related to an underestimate of the ECC concentrations in the stratosphere above 50 hPa. Differences between TOC measured by homogenized ECC and satellite observations show a smaller bias of -1%. Comparisons between homogenized ECC and OHP stratospheric lidar and MLS observations below 26 km are slightly negative (-2%) or positive (+2%), respectively. Both the comparisons with lidar and15satellite observations suggest that homogenization increases the negative bias of the ECC to values lower than -6% above 28km. The reason for this bias is still unclear, but a possible explanation might be related to freezing or evaporation of the sonde solution in the stratosphere.
The warm core of hurricanes as measured by microwave temperature sounders has been related to various azimuthally averaged measures of hurricane strength by several researchers Unfortunately, the use of these instruments (e.g. the Microwave Sounding Units, MSU) for the routine monitoring of tropical cyclone genesis and intensity has been hampered by poor resolution. The recent launch of the NOAA-15 AMSU represents a significant advance in our ability to monitor subtle atmospheric temperature variations (0.1-0.2 C) at relatively high spatial resolution (50 km) in the presence of clouds. Of particular interest is the possible capability of the AMSU to observe the slight warming associated with depression formation, and the relationship of the spatial characteristics of the warming to the surface pressure and wind field, without azimuthal averaging. In order to present the AMSU data as imagery, we have developed a method for precise limb-correction of all 15 AMSU channels. Through a linear combination of several neighboring channels, we can very closely match the nadir weighting functions of a given AMSU sounding channel with the non-nadir data. It is found that there is discernible, localized upper tropospheric warming associated with depression formation in the Atlantic basin during the 1998 hurricane season. Also, it is found that uncertainty in positioning of tropical cyclone circulation centers can be reduced, as in the example of Hurricane Georges as it approached Cuba. Finally, to explore the potential utility of a future high resolution microwave temperature sounder, we present an analysis of the relationship between the modeled surface wind field and simulated high -resolution AMSU-type measurements, based upon cloud resolving model simulations of hurricane Andrew in 1992.
Temperature and ozone data from the Microwave Limb Sounder (MLS) instrument on Upper Atmosphere Research Satellite (UARS) are used to analyze the variability of Kelvin wave activity during the first two years of the UARS mission. The analysis is carried out using the asynoptic mapping technique. Time frequency plots for zonal wavenumbers 1 and 2, at two heights representing the middle stratosphere and the stratopause, respectively, are used to analyze the temporal variability of the waves, and its possible relationship to the equatorial quasi-biennial oscillation (QBO) and semiannual oscillation (SAO). Kelvin wave activity reaches a maximum during the solstice seasons and almost disappears during the equinoxes, in agreement with previous studies. Eastward propagating variance is estimated for wave periods from 4 to 20 days, at all UARS pressure surfaces currently available for MLS. The semiannual modulation of variance is observed to extend down to the lower limits of the height ranges of the temperature and ozone retrievals. Furthermore, a superposed QBO modulation is detected up to the stratopause. Comparison between the variance in eastward propagating waves and the mean zonal wind shows a possible participation of kelvin waves in the forcing of the QBO. At the stratopause the role of Kelvin waves in forcing the SAO appears to be limited, in agreement with previous results. Between the 21-hPa and 4.6-hPa surfaces there appears to be a transition zone where there is no clear relationship between Kelvin wave activity and mean zonal flow acceleration.
An ozone climatology for the period April 1992 to March 1993 and covering pressures from 0.1 to 100 hPa and from 80 deg N to 80 deg S is derived from satellite-based measurements by the Stratospheric Aerosol and Gas Experiment (SAGE), the Halogen Occultation Experiment (HALOE), and the Microwave Limb Sounder (MLS). At pressures less than 1 hPa, separate distributions are given for daytime and nighttime conditions. From 0.46 to 32 hPa the accuracy of the distribution is estimated to be 5%, and the precision is also approx. 5%. Estimates of atmospheric variability are provided on the basis of standard deviations of the measurements within months. Distributions of ozone monthly means and standard deviations are also given in a potential temperature, equivalent latitude coordinate system. This data set is included in the UARS reference atmosphere, and it is accessible through that web site.
We have found that image data acquired with NASA's airborne Thermal Infrared Multispectral Scanner (TIMS) can be used to make estimates of the SO2 content of volcanic plumes. TIMS image data are most applicable to the study of partially transparent SO2 plumes, such as those released during quiescent periods or nonexplosive eruptions. The estimation procedure is based on the LOWTRAN 7 radiative transfer code, which we use to model the radiance perceived by TIMS as it views the ground through an SO2 plume. The input to the procedure includes the altitudes of the aircraft and ground, the altitude and thickness of the SO2 plume, the emissivity of the ground, and altitude profiles of the atmospheric pressure, temperature, and relative humidity. We use the TIMS data to estimate both ground temperatures beneath a plume and SO2 concentrations within a plume. Applying our procedure to TIMS data acquired over Mount Etna, Sicily, on July 29, 1986, we estimate that the SO2 flux from the volcano was approximately 6700 t d(exp -1). The use of TIMS to study SO2 plumes represents a bridge between highly localized methods, such as correlation spectroscopy or direct sampling, and small-scale mapping techniques involving satellite instruments such as the Total Ozone Mapping Spectrometer or Microwave Limb Sounder. We require further airborne experiments to refine our estimation procedure. This refinement is a necessary preparation for the schedueled 1998 launch of the Advanced Spaceborne Thermal Emission and Reflectance Radiometer, which will allow large-scale multispectral thermal infrared image data to be collected over virtually any volcano on Earth at least once every 16 days.
The gravity wave (GW)-resolving capabilities of 118-GHz saturated thermal radiances acquired throughout the stratosphere by the Microwave Limb Sounder (MLS) on the Aura satellite are investigated and initial results presented. Because the saturated (optically thick) radiances resolve GW perturbations from a given altitude at different horizontal locations, variances are evaluated at 12 pressure altitudes between 21 and 51 km using the 40 saturated radiances found at the bottom of each limb scan. Forward modeling simulations show that these variances are controlled mostly by GWs with vertical wavelengths z 5 km and horizontal along-track wavelengths of y 100-200 km. The tilted cigar-shaped three-dimensional weighting functions yield highly selective responses to GWs of high intrinsic frequency that propagate toward the instrument. The latter property is used to infer the net meridional component of GW propagation by differencing the variances acquired from ascending (A) and descending (D) orbits. Because of improved vertical resolution and sensitivity, Aura MLS GW variances are 5?8 times larger than those from the Upper Atmosphere Research Satellite (UARS) MLS. Like UARS MLS variances, monthly-mean Aura MLS variances in January and July 2005 are enhanced when local background wind speeds are large, due largely to GW visibility effects. Zonal asymmetries in variance maps reveal enhanced GW activity at high latitudes due to forcing by flow over major mountain ranges and at tropical and subtropical latitudes due to enhanced deep convective generation as inferred from contemporaneous MLS cloud-ice data. At 21-28-km altitude (heights not measured by the UARS MLS), GW variance in the tropics is systematically enhanced and shows clear variations with the phase of the quasi-biennial oscillation, in general agreement with GW temperature variances derived from radiosonde, rocketsonde, and limb-scan vertical profiles.