Frank D. Palluconi

Martian North Pole Summer Temperatures: Dirty Water Ice

Broadband thermal and reflectance observations of the martian north polar region in late summer yield temperatures for the residual polar cap near 205 K with albedos near 43 percent. The residual cap and several outlying smaller deposits are water ice with included dirt; there is no evidence for any permanent carbon dioxide polar cap.

Thermal inertia mapping of Mars from 60°S to 60°N

Twenty-micrometer brightness temperatures are used to derive the thermal inertia for 81% of the Martian surface between latitudes ±60°. These data were acquired by the two Viking Infrared Thermal Mappers in 1977 and 1978 following the two global dust storms of 1977. The spatial resolution used is 2° in latitude by 2° in longitude and the total range in derived inertia is 1 to 15 × 10−3 cal cm−2 sec−12°K−1. The distribution of thermal inertia is strongly bimodal with all values of thermal inertia less than 4 × 10−3 cal cm−2 sec−12°K−1 being associated with three disjoint bright regions mostly in the northern hemisphere. Sufficient dust is raised in global storms to provide fine material adequate to produce these low-inertia areas but the specific deposition mechanism has not been defined. At the low resolution used, no complete exposures of clean rock were found. There is some tendency for darker material to be associated with higher thermal inertia, although the trend is far from one to one. The distribution of high- and low-inertia areas is sufficiently nonrandom to produce a variation in whole-disk brightness temperature with central meridian longitude. This variation and the change in surface kinetic temperature associated with dust storms are factors in establishing the whole-disk brightness temperature at radio and infrared wavelengths and will be important for those who use Mars as a calibration source.

Overview of the Mars Global Surveyor mission

The Mars Global Surveyor spacecraft was placed into Mars orbit on September 11, 1997, and by March 9, 1999, had slowly circularized through aerobraking to a Sun-synchronous, near-polar orbit with an average altitude of 378 km. The science payload includes the Mars Orbiter Camera, Mars Orbiter Laser Altimeter, Thermal Emission Spectrometer, Ultrastable Oscillator (for Radio Science experiments), and Magnetometer/Electron Reflectometer package. In addition, the spacecraft accelerometers and horizon sensors were used to study atmospheric dynamics during aerobraking. Observations are processed to standard products by the instrument teams and released as documented archive volumes on 6-month centers by the Planetary Data System. Significant results have been obtained from observations of the interior, surface, and atmosphere. For example, Mars does not now have an active magnetic field, although strong remanent magnetization features exist in the ancient crust. These results imply that an internal dynamo ceased operation early in geologic time. Altimetry and gravity data indicate that the crust is thickest under the south pole, thinning northward from the cratered terrain to the northern plains. Analysis of altimetry data demonstrates that Mars is “egg-shaped” with gravitational equipotential contours that show that channel systems in the southern highlands drained to the north, largely to the Chryse trough. A closed contour in the northern plains is consistent with the existence of a great northern ocean. Emission spectra of low-albedo regions show that basaltic rocks dominate spectral signatures on the southern highlands, whereas basaltic andesites dominate the northern lowlands. The bright regions show nondiagnostic spectra, similar to that of dust in the atmosphere. Signatures of aqueous minerals (e.g., clays, carbonates, and sulfates) are noticeably absent from the emission spectra. High spatial resolution images show that the surface has been extensively modified by wind and that layering is nearly ubiquitous, implying that a complex history of events is recorded in surface and near-surface materials. Altimetry data imply that both permanent caps are composed of water ice and dust, with seasonal covers of carbon dioxide frost. Finally, the altimetry data, coupled with thousands of atmospheric profiles, are providing new boundary conditions and dynamic controls for the generation and testing of more realistic dynamic models of the global circulation of the atmosphere.

Validation of a web-based atmospheric correction tool for single thermal band instruments

An atmospheric correction tool has been developed on a public access web site for the thermal band of the Landsat-5 and Landsat-7 sensors. The Atmospheric Correction Parameter Calculator uses the National Centers for Environmental Prediction (NCEP) modeled atmospheric global profiles interpolated to a particular date, time and location as input. Using MODTRAN radiative transfer code and a suite of integration algorithms, the site-specific atmospheric transmission, and upwelling and downwelling radiances are derived. These calculated parameters can be applied to single band thermal imagery from Landsat-5 Thematic Mapper (TM) or Landsat-7 Enhanced Thematic Mapper Plus (ETM+) to infer an at-surface kinetic temperature for every pixel in the scene. The derivation of the correction parameters is similar to the methods used by the independent Landsat calibration validation teams at NASA/Jet Propulsion Laboratory and at Rochester Institute of Technology. This paper presents a validation of the Atmospheric Correction Parameter Calculator by comparing the top-of-atmosphere temperatures predicted by the two teams to those predicted by the Calculator. Initial comparisons between the predicted temperatures showed a systematic error of greater then 1.5K in the Calculator results. Modifications to the software have reduced the bias to less then 0.5 ± 0.8K. Though not expected to perform quite as well globally, the tool provides a single integrated method of calculating atmospheric transmission and upwelling and downwelling radiances that have historically been difficult to derive. Even with the uncertainties in the NCEP model, it is expected that the Calculator should predict atmospheric parameters that allow apparent surface temperatures to be derived within ±2K globally, where the surface emissivity is known and the atmosphere is relatively clear. The Calculator is available at http://atmcorr.gsfc.nasa.gov.

Atmospheric correction of ASTER

An atmospheric correction algorithm for operational use for the high-spatial resolution, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is presented. The correction is a straightforward approach relying on inputs from other satellite sensors to determine the atmospheric characteristics of the scene to be corrected. Methods for the solar reflective and thermal infrared (TIR) are presented separately. The solar-reflective approach uses a lookup table (LUT) based on output from a Gauss-Seidel iteration radiative transfer code. A method to handle adjacency effects is included that relies on model output, assuming a checkerboard surface. An example of a numerical simulation shows that the effect of a land surface on the radiance over the ocean is stronger just off the coastal zone and decreases exponentially with increasing distance from the land. A typical numerical simulation is performed over the Tsukuba lake area in Japan. The TIR approach relies on the radiative transfer code Moderate Resolution Atmospheric Radiance and Transmittance Model (MODTRAN). The code is run for a given set of atmospheric conditions for multiple locations in the scene for several representative elevations. Pixel-by-pixel radiances are then found using spatial interpolation. Sensitivity analysis of the methods indicate that the results of the atmospheric correction will be limited by the accuracies of the input parameters.

The advanced spaceborne thermal emission and reflectance radiometer (Aster)

The Advanced Spaceborne Thermal Emission Reflectance Radiometer (ASTER) is the only high‐spatial‐resolution multispectral imager scheduled to fly in Earth orbit on the first platform of NASAs Earth Observation System (EOS‐A). The instrument will nave three bands in the visible near infrared with 15‐m spatial resolution, six bands in the short‐wave infrared with 30‐m spatial resolution and five bands in the thermal infrared with 90‐m spatial resolution. There will be an additional band in the near infrared with 15‐m spatial resolution that will provide same‐orbit stereo data when combined with the corresponding nadir viewing band. The ASTER instrument is being built by the Japanese Government based on the scientific requirements of the ASTER science team. This team consists of Japanese and American scientists, who will also be responsible for the development of algorithms for data reduction and analysis. The ASTER will be able to address a variety of science objectives identified by the EOS global change program. ASTER will provide surface temperatures and emissivity estimates, surface reflected radiances and digital elevation models at a spatial scale that will allow detailed process studies for MODIS and other global monitoring instruments at the subpixel level. Existing aircraft instruments can be used to simulate data that will be provided by ASTER. Examples are shown here of surface temperature mapping, surface compositional mapping, and digital elevation models derived from the NASA Thermal Infrared Multispectral Scanner, the Airborne Visible Infrared Imaging Spectrometer, and aerial photography.

Infrared Thermal Mapping of the Martian Surface and Atmosphere: First Results

The Viking infrared thermal mapper measures the thermal emission of the martian surface and atmosphere and the total reflected sunlight. With the high resolution and dense coverage being achieved, planetwide thermal structure is apparent at large and small scales. The thermal behavior of the best-observed areas, the landing sites, cannot be explained by simple homogeneous models. The data contain clear indications for the relevance of additional factors such as detailed surface texture and the occurrence of clouds. Areas in the polar night have temperatures distinctly lower than the CO2 condensation point at the surface pressure. This observation implies that the annual atmospheric condensation is less than previously assumed and that either thick CO2 clouds exist at the 20-kilometer level or that the polar atmosphere is locally enriched by noncondensable gases.

Saturn's rings - A survey.

Abstract In this review paper we first discuss the dimensions of major ring features and of the disk of the planet. We then summarize the observed photometric parameters, and because frozen H 2 O appears to be a major ring constituent, we compare the appropriate photometric properties of various forms of snow with those of the ring. We examine several ring models, noting certain characteristics that any model should supply. In our view, a physical means of accounting for the observed ring thickness of ∼2 km is a prime requirement. There appears to be one model that presents no clear observational or theoretical inconsistency. Finally, we list certain problems whose solutions should broaden our knowledge of the ring system.

Autonomous atmospheric compensation (AAC) of high resolution hyperspectral thermal infrared remote-sensing imagery

Atmospheric emission and absorption significantly modify the thermal infrared (TIR) radiation spectra from Earths land surface. A new algorithm, autonomous atmospheric compensation (AAC), was developed to estimate and compensate for the atmospheric effects. The algorithm estimates from hyperspectral TIR measurements two atmospheric index parameters, the transmittance ratio, and the path radiance difference between strong and weak absorption channels near the 11.73 /spl mu/m water band. These two parameters depend on the atmospheric water and temperature distribution profiles, and thus, from them, the complete atmospheric transmittance and path radiance spectra can be predicted. The AAC algorithm is self-contained and needs no supplementary data. Its accuracy depends largely on instrument characteristics, particularly spectral and spatial resolution. Atmospheric conditions, especially humidity and temperature, and other meteorological parameters, also have some secondary impacts. The AAC algorithm was successfully applied to a hyperspectral TIR data set, and the results suggest its accuracy is comparable to that based on the in situ radiosonde measurements.

Vicarious calibration of ASTER thermal infrared bands

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on the Terra satellite has five bands in the thermal infrared (TIR) spectral region between 8-12 /spl mu/m. The TIR bands have been regularly validated in-flight using ground validation targets. Validation results are presented from 79 experiments conducted under clear sky conditions. Validation involved predicting the at-sensor radiance for each band using a radiative transfer model, driven by surface and atmospheric measurements from each experiment, and then comparing the predicted radiance with the ASTER measured radiance. The results indicate the average difference between the predicted and the ASTER measured radiances was no more than 0.5% or 0.4 K in any TIR band, demonstrating that the TIR bands have exceeded the preflight design accuracy of <1 K for an at-sensor brightness temperature range of 270-340 K. The predicted and the ASTER measured radiances were then used to assess how well the onboard calibration accounted for any changes in both the instrument gain and offset over time. The results indicate that the gain and offset were correctly determined using the onboard blackbody, and indicate a responsivity decline over the first 1400 days of the Terra mission.