Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Precision spectroscopy”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Design and Performance of the Hitomi/XRISM Adiabatic Demagnetization Refrigerator Controller

The Resolve instrument in the recently launched X-ray Imaging and Spectroscopy Mission (XRISM) is a rebuild of the Soft X-ray Spectrometer (SXS) in Hitomi (aka Astro-H which had an unfortunately brief mission life in 2016). It is a high-resolution non-dispersive soft x-ray spectrometer from nominally 0.3 keV to 12 keV based on a calorimeter detector array operating at 50 mK with a resolution better than 7 eV FWHM at 6 keV. For such sensitive cryogenic instruments, temperature stability has a strong impact on the detector’s performance. The Adiabatic Demagnetization Refrigerator Controller (ADRC) in the XRISM Resolve instrument is an electronics box responsible for high-precision sub-K temperature readout and control of the multi-stage adiabatic demagnetization refrigerator subsystem to achieve a thermal stability better than 2.5 uK RMS (over a 10-minute interval) for the calorimeter detectors in both cryogen (liquid helium) and cryo-free modes. It has direct telemetry/command and power interfaces with the spacecraft. It also provides sensor read-out and heater circuits for decontamination of the filters in the cold aperture. As a part of the discussion on the design and performance of the ADRC, this paper will also include an overall view of the 50 mK temperature control, plus monitor and control of the aperture filter temperature for de-contamination purpose.

ADRC↗
NASA NTRS1993

Accurate oscillator strengths for interstellar ultraviolet lines of Cl I

Analyses on the abundance of interstellar chlorine rely on accurate oscillator strengths for ultraviolet transitions. Beam-foil spectroscopy was used to obtain f-values for the astrophysically important lines of Cl I at 1088, 1097, and 1347 A. In addition, the line at 1363 A was studied. Our f-values for 1088, 1097 A represent the first laboratory measurements for these lines; the values are f(1088)=0.081 +/- 0.007 (1 sigma) and f(1097) = 0.0088 +/- 0.0013 (1 sigma). These results resolve the issue regarding the relative strengths for 1088, 1097 A in favor of those suggested by astronomical measurements. For the other lines, our results of f(1347) = 0.153 +/- 0.011 (1 sigma) and f(1363) = 0.055 +/- 0.004 (1 sigma) are the most precisely measured values available. The f-values are somewhat greater than previous experimental and theoretical determinations.

Schectman, R. M.↗
NASA NTRS1979

The origin of KREEP

KREEP is a lunar material having very high concentrations of incompatible elements; its name is an acronym for the incompatibles K, rare-earth elements (REE), and P. Although a few pristine (endogenously igneous) KREEPy samples were returned from the Apollo 15 and 17 sites, most KREEPy samples are polymict breccias. Most models of KREEP petrogenesis have been based on partial melting of a variety of sources. Such models fail to explain the veritable absence of variations in incompatible element patterns over the sampled portion of the moon. We have defined a KREEP component based on the average composition of Apollo 14 breccias having extremely high concentrations of incompatible elements. Normalization of accurate incompatible data for KREEPy samples from the Apollo 12, 14, 15, 16, and 17 sites to this component virtually always shows no resolvable fractionation (e.g., <10% variation in the La/Lu ratio), whereas partial melting models typically produce larger fractionations (±20–25% in La/Lu) from a factor of 2 difference in degree of partial melting. Required is a single major source that could provide KREEP to widely separated locations on the nearside of the moon. The anorthositic crust of the moon is commonly attributed to the flotation of plagioclase on a deep, moon-wide magma ocean. Fractional crystallization of this magma ocean would have produced large enrichments of incompatibles in a residual liquid. No other plausible major source of incompatibles has been proposed. We borrow the German prefix ur—meaning primeval and designate this residual liquid ‘urKREEP.’ We propose that all KREEPy rocks originated by dilution of urKREEP with crustal or mantle materials during assimilation, or zone-refining (pristine samples), or impact-induced brecciation (breccias and melt rocks). The formation of urKREEP cannot be dated precisely. Correction of breccia Rb-Sr model ages for Rb loss or gain during the early intense bombardments yields ages that cluster in the range 4.4–4.5 Gy. This implies that crystallization of the magma ocean was essentially complete at this time and is in general agreement with U-Pb evidence indicating crustal formation at 4.4 Gy. Assuming that the moon had the composition of an H-group chondrite depleted in Fe-Ni and FeS and that half the incompatibles fractionated into materials other than urKREEP, the thickness of a moon-wide urKREEP layer was <2 km. Thorium concentrations determined by gamma ray spectroscopy indicate that about 4% of the incompatibles in an H chondritic moon are now in the outermost kilometer.

Paul H. Warren↗
NASA NTRS1993

Microwave digestion preparation and ICP determination of boron in human plasma

A microwave digestion procedure, followed by Inductively Coupled Argon Plasma Spectroscopy, is described for the determination of boron (B) in human plasma. The National Institute of Standards and Technology (NIST) currently does not certify the concentration of B in any substance. The NIST citrus leaves 1572 (CL) Standard Reference Material (SRM) and wheat flour 1567a (WF) were chosen to determine the efficacy of digestion. CL and WF values compare favorably to those obtained from an open-vessel, wet digestion followed by ICP, and by neutron activation and mass spectrometric measurements. Plasma samples were oxidized by doubled-distilled ultrapure HNO3 in 120 mL PFA Teflon vessels. An MDS-81D microwave digestion procedure allows for rapid and relatively precise determination of B in human plasma, while limiting handling hazards and sources of contamination.

Ferrando, A. A.↗
NASA NTRS2014

Near Infrared Cavity Ring-Down Spectroscopy for Isotopic Analyses of CH4 on Future Martian Surface Missions

A compact Near Infrared Continuous Wave Cavity Ring-Down Spectrometer (near-IR-cw-CRDS) was developed as a candidate for future planetary surface missions. The optical cavity was made of titanium with rugged quartz windows to protect the delicate super cavity from the harsh environmental changes that it would experience during space flight and a Martian surface mission. This design assured the long-term stability of the system. The system applied three distributed feedback laser diodes (DFB-LD), two of which were tuned to the absorption line peaks of (sup 12)CH4 and (sup 13)CH4 at 6046.954 inverse centimeters and 6049.121 inverse centimeters, respectively. The third laser was tuned to a spectral-lines-free region for measuring the baseline cavity loss. The multiple laser design compensated for typical baseline drift of a CRDS system and, thus, improved the overall precision. A semiconductor optical amplifier (SOA) was used instead of an Acousto-Optic Module (AOM) to initiate the cavity ring-down events. It maintained high acquisition rates such as AOM, but consumed less power. High data acquisition rates combined with improved long-term stability yielded precise isotopic measurements in this near-IR region even though the strongest CH4 absorption line in this region is 140 times weaker than that of the strongest mid-IR absorption band. The current system has a detection limit of 1.4 times 10( sup –12) inverse centimeters for (sup 13)CH4. This limit corresponds to approximately 7 parts per trillion volume of CH4 at 100 Torrs. With no further improvements the detection limit of our current near IR-cw-CRDS at an ambient Martian pressure of approximately 6 Torrs (8 millibars) would be 0.25 parts per billion volume for one 3.3 minute long analysis.

portable nir crds↗
NASA NTRS2022

Full Spectrum Fitting Analysis of Bulk Elemental Composition Analyzer (BECA) Gamma Ray Data

The Bulk Elemental Composition Analyzer (BECA) is an instrument developed through NASA’s Development and Advancement of Lunar Instrumentation (DALI) program to measure the in situ bulk elemental composition of the lunar regolith from either a lander or rover platform. BECA uses active neutron and gamma ray spectroscopy to make these measurements and thus consists of a Pulsed Neutron Generator (PNG), a CeBr3 scintillator Gamma Ray Spectrometer (GRS), and two He-3 neutron detectors. As shown in Figure 1, the PNG emits 14.1 MeV neutrons that induce lunar materials to emit gamma rays with energies characteristic of the elements that produced them. The GRS measures the energy spectra of these gamma rays to identify the elements present and establish their absolute concentrations in the regolith. The analysis of BECA’s gamma ray spectral data yields quantitative elemental concentrations by mass (wt.%) in the material directly beneath the lunar lander or rover. A Compact Neutron Monitor (CNM) attached to the PNG precisely measures the output of 14.1 MeV neutrons to enable quantification of absolute elemental abundances.

Mauricio Ayllon Unzueta↗
NASA NTRS2018

Dating Igneous Rocks Using the Potassium–Argon Laser Experiment (KArLE) Instrument: A Case Study for ~380 Ma Basaltic Rocks

We report new K–Ar isochron data for two ~380 Ma basaltic rocks, using an updated version of the Potassium–Argon Laser Experiment (KArLE), which is being developed for future in situ dating of planetary materials. These basalts have K contents comparable with those of lunar KREEP basalts or igneous lithologies found by Mars rovers, whereas previous proof‐of‐concept studies focused primarily on more K‐rich rocks. We aim to measure these analogous samples to show the advancing capability of in situ K–Ar geochronology. Combining laser‐induced breakdown spectroscopy (LIBS), mass spectrometry (MS), and microscopic analyses, we measured the abundance of K and 40Ar from 23 spots on the basalt samples. We then constructed K–Ar isochron plots from these rocks. The breadboard instrument consists of flight‐equivalent devices including a 30‐mJ Nd:YAG laser and a quadrupole mass spectrometer. Despite much lower K abundances than in previous studies, the isochron slopes yielded 380 ± 44 Ma and 398 ± 50 Ma for 380.7‐Ma and 373.5‐Ma rocks, respectively, indicating that accuracy better than 25 Ma (<7%) is achievable with our instrument. The isochron intercepts both yielded trapped 40Ar approximately 1 × 10−6 cm3 STP/g. Our experimental results demonstrate that accurate and precise measurements are possible using the KArLE approach on basaltic rocks, which are ubiquitous on planetary surfaces, and are useful in addressing a wide range of questions in planetary science.

Yuichiro Cho↗
NASA NTRS1993

Imaging with INTEGRAL

The INTEGRAL mission was proposed in response to the ESA M2 call for proposals and is dedicated to the fine spectroscopy and imaging of celestial gamma-ray sources in the energy range 15 keV to 10 MeV. Cosmic gamma-rays are emitted on a wide range of angular scales and structures for a diverse population of astronomical objects. The emission, which includes discrete spectral lines and continuum radiation is derived from point sources, localized regions, as well as a diffuse band along the Galactic plane. Much of the gamma-ray sky is composed from transient phenomena which range from the few second timescale associated with gamma-ray bursts to larger lived events lasting some days or more. These class of events pose the challenge of firstly identification and secondly that of precise positional location of 'random' short lived events which arrive isotropically. In this article the imaging requirements are evaluated in light of current observational astronomical data and practical solutions for the INTEGRAL telescope are discussed. Some of the key problems are highlighted.

Dean, A. J.↗
NASA NTRSDate not supplied

Wavelength Calibration of the Full-sun Ultraviolet Rocket SpecTrograph: (FURST)

The Sun has a well-known periodicity in sunspot number and magnetic field variation. The underlying cause of this 11-year cycle is not fully understood and has yet to be connected with those processes in other stellar objects. The Full-sun Ultraviolet Rocket SpecTrograph (FURST) is a sounding rocket payload being developed by Montana State University (MSU) alongside the Marshall Space Flight Center (MSFC) solar physics group. Scheduled to launch from White Sands Missile Range (WSMR) in 2022, this instrument is unique in that it will provide the connection between stellar observatories with measurements of our Sun. It will achieve this through extremely high-resolution full-disk spectroscopy in EUV. We aim to obtain a wavelength resolution R > 10,000 in the 115 - 181 nm range, on par with that of the Hubble (HST) Space Telescope Imaging Spectrograph (STIS). The Lyman Alpha line (121 nm) is known to oversaturate most CCD electronics and is of particular challenge for this spectral range. In addition, this resolution goal will allow us to study the 3 km/s motion (a Doppler-shift of about 0.01 Angstroms) of the relatively low-temperature plasma in the chromosphere and lower corona. This paper will present the results of our simulation of the diagnostic lamp signal to be used in this wavelength calibration. To test the viability of this precise of a device, we are building a collimator capable of calibrating the FURST instrument under these strict radiometric requirements. By way of a diagnostic lamp simulation, we will account for photon noise, CCD electronic readout noise, and statistical error. These will lead to the development of our pre- and post-launch calibration plan. Future work includes absolute radiometric and wavelength calibration with this new collimator. In addition, the ability of FURST to measure extremely small Doppler-shifts will provide capabilities for planetary atmospheric scientists. This impact is coupled with the diverse international partnership created by the closely-knit Sounding Rocket teams across the globe. These Sounding Rockets have an even broader impact, as they encourage future satellite missions under the prospect of long-term observations.

FURST↗
NASA NTRS1993

Goniospectrometric properties of a white standard

Reflection spectroscopy is one of the fundamental tools in planetary remote sensing. Most of the laboratory work is done in terms of bidirectional reflectance R in the wavelength range of reflected sunlight (250 nm - 2500 nm). Bidirectional reflectance R is defined as the radiance of a surface relative to the radiance of an ideal Lambertian reflector, identically illuminated (radiance coefficient). For quantitative laboratory work the absolute scale of R has to be known. In addition, for many purposes it is necessary to know the dependence of R from phase angle for a large range of geometries. In many cases, this can only be achieved if the goniospectrometric properties of the white standard that is used are known with high precision. For a long time Halon has been used as a white standard by most laboratories. Because Halon is no more available we have now analyzed the goniospectrometric properties of Spectralon SRS-99 with the DLR-goniospectrometer.

Oehler, A.↗
NASA NTRS1996

On the Assessment and Uncertainty of Atmospheric Trace Gas Burden Measurements with High Resolution Infrared Solar Occultation Spectra from Space by the ATMOS Experiment

The Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument is a high resolution Fourier transform spectrometer that measures atmospheric composition from low Earth orbit with infrared solar occultation sounding in the limb geometry. Following an initial flight in 1985, ATMOS participated in the Atmospheric Laboratory for Applications and Science (ATLAS) 1, 2, and 3 Space Shuttle missions in 1992, 1993, and 1994 yielding a total of 440 occultation measurements over a nine year period. The suite of more than thirty atmospheric trace gases profiled includes CO2, O3, N2O, CH4, H2O, NO, NO2, HNO3, HCl, HF, ClONO2, CCl3F, CCl2F2, CHF2Cl, and N2O5. The analysis method has been revised throughout the mission years culminating in the 'version 2' data set. The spectroscopic error analysis is described in the context of supporting the precision estimates reported with the profiles; in addition, systematic uncertainties assessed from the quality of the spectroscopic database are described and tabulated for comparisons with other experiments.

Abrams, M. C.↗
NASA NTRSDate not supplied

Application of High-Spatial Resolution LA-MC-ICP-MS in Planetary Materials

High-precision stable and radiogenic isotopic measurements of planetary materials can help elucidate processes taking place during early Solar System formation, as well as during subsequent planetary differentiation. Laser Ablation Multi Collector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICP-MS) adds the valuable ability of preserving the spatial context of these isotopic measurements, by sampling small sample volumes (~10 – 60 um diameter) using a pulsed laser system. In the Center for Isotope Cosmochemistry and Geochronology (CICG) at NASA Johnson Space Center, these in-situ isotopic measurements are primarily made using the Applied SpectraTM iX-fs-Tandem LA-LIBS Instrument coupled to the Nu InstrumentsTM SP1700 MC-ICP-MS. The instrumental set-up also provides simultaneous Laser Induced Breakdown Spectroscopy (LIBS) measurements and the potential use of a low energy path with a collision/reaction cell for additional interference removal, though we focus here on the typical high-energy LA-MC-ICP-MS operation. We will provide examples of stable (e.g., Mg) and radiogenic (e.g., Lu-Hf) isotopic systems measured in planetary materials and their terrestrial analogs. The measurement of mass dependent Mg isotopic variations is an important tool for reconstructing processes such as evaporation and condensation of solids in the solar nebula. For early Solar System samples, Mg isotope measurements are also important for the short-lived (t1/2 = 0.7 Ma) Al-Mg chronometer. During laser ablation analyses, the measurement of the Al-Mg isotopic system is made in medium mass resolution (RP ~9500 at ~20% transmission) to limit interferences from 48Ti2+ and 48Ca2+ on 24Mg+, in addition to 52Cr2+ and 12C14N+ on 26Mg+. Measured in the mineral zircon, the 176Lu-176Hf decay system is often used for understanding the growth of continents on Earth, and is also a vital aid in deciphering early large-scale planetary differentiation processes, such as the crystallization of the lunar magma ocean, which is thought to be responsible for much of the Moon’s crust. Lu-Hf measurements are made in low resolution mode (RP <2000), with 10 ion masses (from 171Yb to 180Hf) measured simultaneously to facilitate corrections for isobaric interferences from 176Yb and 176Lu on 176Hf.

Jacob B Setera↗
NASA NTRS2006

The Constellation-X Spectroscopy X-ray Telescope: Recent Technology Development

We describe recent progress in the technology development program for the mirror system for the Constellation-X Spectroscopy X-ray Telescope (SXT). Development of this mirror represents a significant technology challenge, as it must provide a combination of large effective area (3 sq. m) and modest angular resolution (15 arc second half power diameter requirement; 5 arc second goal) with a limited mass allocation. The baseline design incorporates over 200 nested Wolter 1 mirrors. Each of these in turn is segmented in order to simplify handling of the mirrors and facilitate mass production. The X-ray reflecting surfaces are fabricated from thin, thermally formed glass sheets. Production improvements have yielded mirror segments that approach the performance requirement without the need for epoxy replication. A mounting and alignment approach incorporating piezoelectric actuators has been shown to manipulate mirror segments with the required precision without introducing significant distortion. Substantial improvements in metrology methodology have provided insights into the mirror segment forming and alignment processes. An X-ray demonstration of a mirror segment pair is planned for early 2006.

Petre, Robert↗
NASA NTRS1995

Raman Spectroscopy as a Method for Mineral Identification on Lunar Robotic Exploration Missions

The sharp, nonoverlapping Raman bands for plagioclase, pyroxene, and olivine would be advantageous for on-surface, active mineralogical analysis of lunar materials. A robust, light-weight, low-power, rover-based Raman spectrometer with a laser exciting source, entirely transmission-mode holographic optics, and a charge-coupled device (CCD) detector could fit within a less than 20 cm cube. A sensor head on the end of an optical fiber bundle that carried the laser beam and returned the scattered radiation could be placed against surfaces at any desired angle by a deployment mechanism; otherwise, the instrument would need no moving parts. A modem micro-Raman spectrometer with its beam broadened (to expand the spot to 50-micrometer diameter) and set for low resolution (7/cm in the 100-1400/cm region relative to 514.5-nm excitation), was used to simulate the spectra anticipated from a rover instrument. We present spectra for lunar mineral grains, less than 1 mm soil fines, breccia fragments, and glasses. From frequencies of olivine peaks, we derived sufficiently precise forsterite contents to correlate the analyzed grains to known rock types and we obtained appropriate forsterite contents from weak signals above background in soil fines and breccias. Peak positions of pyroxenes were sufficiently well determined to distinguish among orthorhombic, monoclinic, and triclinic (pyroxenoid) structures; additional information can be obtained from pyroxene spectra, but requires further laboratory calibration. Plagioclase provided sharp peaks in soil fines and most breccias even when the glass content was high.

Wang, Alian↗
NASA NTRS2004

Optical Metrology for the Segmented Optics on the Constellation-X Spectroscopy X-Ray Telescope

We present the metrology requirements and metrology implementation necessary to prove out the reflector technology for the Constellation X(C-X) spectroscopy X-ray telescope (SXT). This segmented, 1.6m diameter highly nested Wolter-1 telescope presents many metrology and alignment challenges. In particular, these mirrors have a stringent imaging error budget as compared to their intrinsic stiffness; This is required for Constellation-X to have sufficient effective area with the weight requirement. This has implications for the metrology that can be used. A variety of contract and noncontact optical profiling and interferometric methods are combined to test the formed glass substrates before replication and the replicated reflector segments.The reflectors are tested both stand-alone and in-situ in an alignment tower.Some of these methods have not been used on prior X-ray telescopes and some are feasible only because of the segmented approach used on the SXT. Methods discussed include high precision coordinate measurement machines using very low force or optical probe axial interferometric profiling azimuthal circularity profiling and use of advanced null optics such as conical computer generated hologram (CGHs).

Content, David↗
NASA NTRS2014

The Type IIb Supernova 2013df and its Cool Supergiant Progenitor

We have obtained early-time photometry and spectroscopy of supernova (SN) 2013df in NGC 4414. The SN is clearly of Type II b, with notable similarities to SN 1993J. From its luminosity at secondary maximum light, it appears that less Ni-56 (is approximately less than 0.06M) was synthesized in the SN 2013df explosion than was the case for the SNe II b 1993J, 2008ax, and 2011dh. Based on a comparison of the light curves, the SN 2013df progenitor must have been more extended in radius prior to explosion than the progenitor of SN 1993J. The total extinction for SN 2013dfis estimated to be A(sub V) = 0.30 mag. The metallicity at the SN location is likely to be solar. We have conducted Hubble Space Telescope(HST) Target of Opportunity observations of the SN with the Wide Field Camera 3, and from a precise comparison of these new observations to archival HST observations of the host galaxy obtained 14 yr prior to explosion, we have identified the progenitor of SN 2013df to be a yellow supergiant, somewhat hotter than a red supergiant progenitor for a normal Type II-Plateau SN. From its observed spectral energy distribution, assuming that the light is dominated by one star, the progenitor had effective temperature T(sub eff) = 4250+/-100 K and a bolometric luminosity L(sub bol) =10(exp 4.94+/-0.06) Solar Luminosity. This leads to an effective radius Reff = 545+/-65 Solar Radius. The star likely had an initial mass in the range of 13-17Solar Mass; however, if it was a member of an interacting binary system, detailed modeling of the system is required to estimate this mass more accurately. The progenitor star of SN 2013df appears to have been relatively similar to the progenitor of SN 1993J.

TYPE IIb↗
NASA NTRS2022

Direct-imaging Discovery and Dynamical Mass of a Substellar Companion Orbiting an Accelerating Hyades Sun-like Star with SCExAO/CHARIS

We present the direct-imaging discovery of a substellar companion in orbit around a Sun-like star member of the Hyades open cluster. So far, no other substellar companions have been unambiguously confirmed via direct imaging around main-sequence stars in Hyades. The star HIP 21152 is an accelerating star as identified by the astrometry from the Gaia and Hipparcos satellites. We detected the companion, HIP 21152 B, in multiple epochs using the high-contrast imaging from SCExAO/CHARIS and Keck/NIRC2. We also obtained the stellar radialvelocity data from the Okayama 188 cm telescope. The CHARIS spectroscopy reveals that HIP 21152 B’s spectrum is consistent with the L/T transition, best fit by an early T dwarf. Our orbit modeling determines the semimajor axis and the dynamical mass of HIP 21152 B to be 17 +7.2 −3.8 and 27.8 +8.4 −5.4 M Jub , respectively. The mass ratio of HIP 21152 B relative to its host is ≈2%, near the planet/brown dwarf boundary suggested by recent surveys. Mass estimates inferred from luminosity-evolution models are slightly higher (33–42 MJup). With a dynamical mass and a well-constrained age due to the system’s Hyades membership, HIP 21152 B will become a critical benchmark in understanding the formation, evolution, and atmosphere of a substellar object as a function of mass and age. Our discovery is yet another key proof of concept for using precision astrometry to select direct-imaging targets.

Masayuki Kuzuhara↗
NASA NTRS2017

Retrieval of Water Vapor Column Abundance and Aerosol Properties from ChemCam Passive Sky Spectroscopy

We derive water vapor column abundances and aerosol properties from Mars Science Laboratory (MSL) ChemCam passive mode observations of scattered sky light. This paper covers the methodology and initial results for water vapor and also provides preliminary results for aerosols. The data set presented here includes the results of 113 observations spanning from Mars Year 31 L(s) = 291 deg (March 30, 2013) to Mars Year 33 L(s) = 127 deg (March 24, 2016). Each ChemCam passive sky observation acquires spectra at two different elevation angles. We fit these spectra with a discrete-ordinates multiple scattering radiative transfer model, using the correlated-k approximation for gas absorption bands. The retrieval proceeds by first fitting the continuum of the ratio of the two elevation angles to solve for aerosol properties, and then fitting the continuum-removed ratio to solve for gas abundances. The final step of the retrieval makes use of the observed CO 2 absorptions and the known CO 2 abundance to correct the retrieved water vapor abundance for the effects of the vertical distribution of scattering aerosols and to derive an aerosol scale height parameter. Our water vapor results give water vapor column abundance with a precision of +/-0.6 precipitable microns and systematic errors no larger than +/-0.3 precipitable microns, assuming uniform vertical mixing. The ChemCam-retrieved water abundances show, with only a few exceptions, the same seasonal behavior and the same timing of seasonal minima and maxima as the TES, CRISM, and REMS-H data sets that we compare them to. However ChemCam-retrieved water abundances are generally lower than zonal and regional scale from-orbit water vapor data, while at the same time being significantly larger than pre-dawn REMS-H abundances. Pending further analysis of REMS-H volume mixing ratio uncertainties, the differences between ChemCam and REMS-H pre-dawn mixing ratios appear to be much too large to be explained by large scale circulations and thus they tend to support the hypothesis of substantial diurnal interactions of water vapor with the surface. Our preliminary aerosol results, meanwhile, show the expected seasonal pattern in dust particle size but also indicate a surprising interannual increase in water-ice cloud opacities.

Mcconnochie, Timothy H.↗