Vincent J. Realmuto

Multispectral thermal infrared mapping of the 1 October 1988 Kupaianaha flow field, Kilauea volcano, Hawaii

Multispectral thermal infrared radiance measurements of the Kupaianaha flow field were acquired with the NASA airborne Thermal Infrared Multispectral Scanner (TIMS) on the morning of 1 October 1988. The TIMS data were used to map both the temperature and emissivity of the surface of the flow field. The temperature map depicted the underground storage and transport of lava. The presence of molten lava in a tube or tumulus resulted in surface temperatures that were at least 10° C above ambient. The temperature map also clearly defined the boundaries of hydrothermal plumes which resulted from the entry of lava into the ocean. The emissivity map revealed the boundaries between individual flow units within the Kupaianaha field. In general, the emissivity of the flows varied systematically with age but the relationship between age and emissivity was not unique. Distinct spectral anomalies, indicative of silica-rich surface materials, were mapped near fumaroles and ocean entry sites. This apparent enrichment in silica may have resulted from an acid-induced leaching of cations from the surfaces of glassy flows. Such incipient alteration may have been the cause for virtually all of the emissivity variations observed on the flow field, the spectral anomalies representing areas where the acid attack was most intense.

Quantitative estimation of granitoid composition from thermal infrared multispectral scanner (TIMS) data, Desolation Wilderness, northern Sierra Nevada, California

We have produced images that quantitatively depict modal and chemical parameters of granitoids using an image processing algorithm called MINMAP that fits Gaussian curves to normalized emittance spectra recovered from thermal infrared multispectral scanner (TIMS) radiance data. We applied the algorithm to TIMS data from the Desolation Wilderness, an extensively glaciated area near the northern end of the Sierra Nevada batholith that is underlain by Jurassic and Cretaceous plutons that range from diorite and anorthosite to leucogranite. The wavelength corresponding to the calculated emittance minimum λmin varies linearly with quartz content, SiO2, and other modal and chemical parameters. Thematic maps of quartz and silica content derived from λmin values distinguish bodies of diorite from surrounding granite, identify outcrops of anorthosite, and separate felsic, intermediate, and mafic rocks.

Impact of atmospheric water vapor on the thermal infrared remote sensing of volcanic sulfur dioxide emissions: A case study from the Pu'u ‘O’ vent of Kilauea Volcano, Hawaii

The December 18, 1999, launch of NASAs Terra satellite put two multispectral thermal infrared imaging instruments into Earth orbit. Experiments with airborne instruments have demonstrated that the data from such instruments can be used to detect volcanic SO2 plumes and clouds. However, one of the greatest challenges that will confront efforts to monitor volcanic SO2 emissions from space is the need to characterize the local atmosphere. In this paper we evaluate the sensitivity of the SO2 retrieval procedure to our knowledge of the local atmospheric conditions. We compare SO2 retrievals obtained with distant (radiosonde) and local (Fourier transform infrared (FTIR) soundings) atmospheric measurements and find that the relative difference is typically ±25%. For ground temperature retrievals the relative difference is ±1.5%. These results lead us to conclude that while local measurements of atmospheric conditions are preferable, useful retrievals can be obtained using atmospheric measurements from distant sites. In addition, we find very good agreement between SO2 and ground temperature retrievals obtained from thermal infrared imagery and FTIR soundings.

A comparison of AIRS, MODIS and OMI sulphur dioxide retrievals in volcanic clouds

Volcanic degassing is a major contributor to the global sulphur dioxide (SO2) budget, characterized by quiescent emissions in the lower troposphere with sporadic, spatially variable explosive eruptions into the upper troposphere and lower stratosphere (UTLS). The volcanic input of SO2 to the atmosphere can be quantified using a suite of satellite-based instruments with a range of orbits and resolutions, resulting in differing estimates of SO2 extent and concentration from eruptions. We compare near-coincident retrievals of SO2 from the Moderate Resolution Imaging Spectroradiometer (MODIS), Atmospheric Infrared Radiation Sounder (AIRS) and Ozone Monitoring Instrument (OMI) at four eruptive settings. The OMI instrument is the most sensitive, with the ability to detect both low and high altitude clouds, but as an ultraviolet sensor, retrievals are limited to daytime, unlike the infrared sensors. AIRS retrievals are up to an order of magnitude less sensitive than OMI, restricted to water-free clouds in the upper troposphere. MODIS has the lowest sensitivity and is therefore constrained to the largest eruptions. Total tonnages from each sensor reflect these varying sensitivities along with potential calibration discrepancies. Results suggest that by using a number of instruments in synergy a more complete method of eruption detection is achieved.

Recovery of spectral emissivity from Thermal Infrared Multispectral Scanner imagery acquired over a mountainous terrain: A case study from Mount Etna Sicily

The estimation of ground radiance and emissivity from Thermal Infrared Multispectral Scanner (TIMS) data is strongly dependent on the atmospheric correction applied to these data. Since such corrections are a function of the atmospheric path between the sensor and ground, correction techniques that do not consider the topographic variations within a scene can introduce appreciable error in the estimation of the atmosphere effects. In this paper, we describe the development and application of a variable-elevation atmospheric correction procedure. Our objective was to incorporate changes in target altitude into a general atmosphere correction strategy. This procedure was tested on a TIMS data set acquired over Mt. Etna, Italy in July 1986. The methodology adopted in this study is based on the use of the LOWTRAN radiative transfer code and a digital elevation model (DEM) registered to the image data. The image data are divided into a series of layers, based on elevation, and a separate atmosphere correction is applied to each layer. Maps of emissivity estimates derived with the variable-elevation approach were compared with geologic maps of the Etna flow fields. Prior to the variable-elevation correction, the emissivity spectra of long lava flows appeared to vary with elevation. Following the variable-elevation correction, many of these spectral artifacts were removed from the emissivity maps. In addition, the variable-elevation correction increased our ability to discriminate individual lava flows.

Observations of SO2 production and transport from Bezymianny volcano, Kamchatka using the MODerate resolution Infrared Spectroradiometer (MODIS)

Bezymianny volcano, Kamchatka Peninsula, Russia, is one of the most active volcanoes in the North Pacific (NOPAC) region and erupts violently on average every 6 months. We report the SO2 cloud mass, emission and transport rates for the eruption of Bezymianny on 13–14 January 2004, and discuss the issues associated with determining SO2 production and transfer to the atmosphere from NOPAC volcanoes. During the 13–14 January 2004 eruption, Bezymianny was observed twice by the MODerate Resolution Imaging Spectroradiometer (MODIS) at 0025 and 0210 UTC on 14 January. Using a retrieval based on the 8.6 µm SO2 infrared absorption feature, MODIS yielded a total cloud mass of 34.6±5.19 kt of SO2, an SO2 emission rate of ∼(4.9×103)±(9.12×102) kg s−1, and a transport rate of ∼16.5 m s−1. We tested the sensitivity of the SO2 algorithm to the following input parameters: cloud top height, atmospheric profile, spectral emissivity of the ground and maximum SO2 threshold. The retrieval is sensitive to the atmospheric profile and is particularly dependent on the choice of background emissivity. Multiple background emissivity spectra, obtained over homogeneous backgrounds, reduce errors in the retrieval, when compared to single, less homogeneous emissivity regions.

Thermal infrared spectral imager for airborne science applications

An airborne thermal hyperspectral imager is underdevelopment which utilizes the compact Dyson optical configuration and quantum well infrared photo detector (QWIP) focal plane array. The Dyson configuration uses a single monolithic prism-like grating design which allows for a high throughput instrument (F/1.6) with minimal ghosting, stray-light and large swath width. The configuration has the potential to be the optimal imaging spectroscopy solution unmanned aerial vehicles (UAV) due to its small form factor and relatively low power requirements. The planned instrument specifications are discussed as well as design trade-offs. Calibration testing results (noise equivalent temperature difference, spectral linearity and spectral bandwidth) and laboratory emissivity plots from samples are shown using an operational testbed unit which has similar specifications as the final airborne system. Field testing of the testbed unit was performed to acquire plots of emissivity for various known standard minerals (quartz). A comparison is made using data from the ASTER spectral library.

Towards HyTES: an airborne thermal imaging spectroscopy instrument

An airborne thermal hyperspectral imager is underdevelopment which utilizes the compact Dyson optical configuration and quantum well infrared photo detector (QWIP) focal plane array. The Dyson configuration uses a single monolithic prism-like grating design which allows for a high throughput instrument (F/1.6) with minimal ghosting, stray-light and large swath width. The configuration has the potential to be the optimal imaging spectroscopy solution unmanned aerial vehicles (UAV) due to its small form factor and relatively low power requirements. The planned instrument specifications are discussed as well as design trade-offs. Calibration testing results (noise equivalent temperature difference, spectral linearity and spectral bandwidth) and laboratory emissivity plots from samples are shown using an operational testbed unit which has similar specifications as the final airborne system. Field testing of the testbed unit was performed to acquire plots of emissivity for various known standard minerals (quartz). A comparison is made using data from the ASTER spectral library.

AIRS/AMSU/HSB on EOS Aqua: first-year post-launch assessment

The Atmospheric Infrared Sounder (AIRS), Advanced Microwave Sounding Unit (AMSU), and Humidity Sounder from Brazil (HSB) are three instruments onboard the Earth Observing System (EOS) Aqua Spacecraft. Together, they form the Aqua Infrared and Microwave Sounding Suite (AIMSS). This paper discusses the science objectives and the status of the instruments and their data products one year after launch. All instruments went through a successful activation and calibration and have produced exceptional, calibrated, Level 1B data products. The Level 1B Product Generation Executables (PGEs) have been given to NOAA and the GSFC DAAC for production and distribution of data products. After nine months of operations, the HSB instrument experienced an electrical failure of the scanner. Despite the loss of HSB, early validation results have shown the AIRS and AMSU are producing very good temperature profiles.

Remote sensing atmospheric trace gases with infrared imaging spectroscopy

Atmospheric pollution affects human health, food production, and ecosystem sustainability, causing environmental and climate change. Species of concern include nitrogen oxides, sulfur dioxide (SO2 ), and the greenhouse gases (GHG) methane (CH4 ) and carbon dioxide (CO2 ). Trace gas remote sensing can provide source detection, attribution, monitoring, hazard alerts, and air quality evaluation.