Thermal Emission Data Research Articles

Hotspots on Venus

![Figure][1] CREDIT: SMREKAR ET AL. The surface of Venus shows clear signs of volcanism, but are there active volcanoes on Venus today? The answer to this question will bear on our understanding of the planet's climate evolution and interior dynamics. Using surface thermal emissivity data returned by the Venus Express spacecraft, Smrekar et al. (p. [605][2], published online 8 April) looked at three hotspots on Venus. These places were identified by analogy with terrestrial hotspots like Hawaii, which are believed to overlie mantle plumes and to be the most likely sites for current volcanic activity. Lava flows at the three hotspots have anomalously high thermal emissions when compared with their surroundings. Low emissivity is generally interpreted as the result of surface alteration by the corrosive atmosphere of Venus. High emissivity implies that not much alteration took place and thus that the hotspots must represent recently active volcanoes younger than 2.5 million years. [1]: pending:yes [2]: /lookup/doi/10.1126/science.1186785

Recent Hotspot Volcanism on Venus from VIRTIS Emissivity Data

The questions of whether Venus is geologically active and how the planet has resurfaced over the past billion years have major implications for interior dynamics and climate change. Nine "hotspots"--areas analogous to Hawaii, with volcanism, broad topographic rises, and large positive gravity anomalies suggesting mantle plumes at depth--have been identified as possibly active. This study used variations in the thermal emissivity of the surface observed by the Visible and Infrared Thermal Imaging Spectrometer on the European Space Agency's Venus Express spacecraft to identify compositional differences in lava flows at three hotspots. The anomalies are interpreted as a lack of surface weathering. We estimate the flows to be younger than 2.5 million years and probably much younger, about 250,000 years or less, indicating that Venus is actively resurfacing.

Assessing the potential of multispectral remote sensing for lithological mapping on the Antarctic Peninsula: case study from eastern Adelaide Island, Graham Land

AbstractThe results of lithological mapping using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data for the Wright Peninsula region of Adelaide Island, Antarctic Peninsula are compared with existing geological maps and recent field observations to assess the potential of multispectral remote sensing to undertake lithological mapping on the Antarctic Peninsula. The Wright Peninsula comprises calc-alkaline intrusive rocks ranging from granite to gabbro, volcanic rocks of acidic to intermediate composition, and arc-related sediments. The reflective and thermal bands of a single ASTER image were analysed with reference to reflectance spectra of rock samples from the study area. Assessment of the ASTER mapping outcomes was undertaken with a newly compiled geological map of Adelaide Island and observations made during recent fieldwork. The results demonstrate that ASTER can uniquely discriminate granitoid intrusive rocks and altered rhyolitic volcanic rocks that display distinctive spectral properties. The results are more ambiguous at discriminating more intermediate/mafic rocks such as diorite/gabbro, andesite/basalt and chlorite-bearing sediments due to the similarity in spectral properties. These results demonstrate that although ASTER data are limited in their ability to uniquely discriminate lithologies they can provide important lithological information in support of geological mapping on the Antarctic Peninsula.

Detecting forest degradation in Kochi, Japan: ground‐based measurements versus satellite (Terra/ASTER) remote sensing

AbstractForest degradation, due mainly to poor management, is of increasing concern in Japan. Major ecosystem functions, such as biodiversity, productivity, and soil and water retention, are being lost or weakened in Japan's forests, especially in Japanese cypress (Hinoki; Chamaecyparis Obtusa Sieb.) plantations. Detecting forest degradation is critical to the restoration of the ecosystem in the Kochi area, but ground‐based detection methods are labour intensive and difficult to implement in mountainous areas. In this study we examined the ecological characteristics (e.g. soil water content (SWC) and leaf water content) of degraded and healthy forests, based on in situ measurements and controlled experiments, and present a new method for mapping forest degradation based on remote sensing techniques. A field survey was carried out to record the locations and conditions of the degraded Japanese cypress plantations. Empirical relationships among the degraded plantation, SWC, fuel moisture content (FMC), and vegetation indices (VIs) were investigated by field survey and control experiments. We found that the SWC of the degraded Japanese cypress plantations was lower than that of the well‐managed Japanese cypress plantations. We also found that the SWC, FMC, and VI are highly correlated (R > 0·80). In addition to the ground investigation, we used the advanced spaceborne thermal emission and reflection radiometer (ASTER) data and compared a number of VIs to determine their relationships to the biophysical/biochemical attributes of vegetation canopies. Our results showed that the ASTER thermal band was the most effective method used to detect degraded Japanese cypress plantations in the study area. Copyright © 2010 John Wiley & Sons, Ltd.

Multi-decadal ice-velocity and elevation changes of a monsoonal maritime glacier: Hailuogou glacier, China

AbstractDigital elevation models (DEMs) of the ablation area of Hailuogou glacier, China, produced from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data obtained in 2009, differential GPS (DGPS) data surveyed in 2008 and aerial photographs acquired in 1966 and 1989 are differenced to estimate long- and short-term glacier surface elevation change (dh/dt). The mean dh/dt of the ablation area over 43 years (1966–2009) is −1.1 ± 0.4 m a−1. Since 1989 the thinning has accelerated significantly. Ice velocities measured by DGPS at 28 fixed stakes implanted in the ablation area increase with distance from the glacier terminus, ranging from 41.0 m a−1 approaching the glacier terminus to a maximum of 205.0 m a−1 at the base of an icefall. Our results reveal that the overall average ice velocity in the ablation area has undergone significant temporal variability over the past several decades. Changes in glacier surface elevation in the ablation area result from the combined effects of climate change and glacier dynamics, which are driven by different factors for different regions and periods.

Spatial Variation of Vegetation Moisture Mapping Using Advanced Spaceborne Thermal Emission & Reflection Radiometer (ASTER) Data

Drought is a recurrent phenomenon in Jharkhand. It affects the livelihoods of the majority of its people, particularly tribals and dalits living in rural areas. Twelve of the 24 districts of the state, covering 43% of the total land area, are covered under the Drought Prone Areas Programme (DPAP). Hunger and starvation deaths are reported almost every year. Vegetation moisture content is one of the key parameters in drought monitoring, agricultural modelling and forest health mapping. In this paper the three different approaches is described using Advanced Spaceborne Thermal Emission & Reflection Radiometer (ASTER) data for measuring the vegetation moisture content in a part of Palamu Commissionaire of Jharkhand state, which is prone to severe drought. ASTER thermal data was used to calculate land surface temperature using Normalized Differential Vegetation Index (NDVI) emissivity correction method. Reflective bands are used to determine NDVI, Modified Soil Adjustment Vegetation Index (MSAVI) & Normalised Differential Water Index (NDWI). The three different vegetation moisture estimation methods namely MSAVI – LST (land surface temperature) feature space identification, NDWI & Vegetation Dryness Index (VDI) is applied to determine the vegetation moisture level. The results of three methods were classified and final moisture content map was produced. The result was validated using rainfall data of study area. This study indicates that by proper pre-processing of ASTER data, it can be used to estimate the land surface temperature and vegetation moisture content and can be used for drought prediction.

A Single-Channel Algorithm for Land-Surface Temperature Retrieval From ASTER Data

This letter presents an adaptation to Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data of the generalized single-channel (SC) algorithm developed by JimE?nez-MuN?oz and Sobrino, also adapted to the Landsat thermal-infrared (TIR) channel (band 6) later by JimE?nez-MuN?oz The SC algorithm relies on the concept of atmospheric functions (AFs), which are dependent on atmospheric transmissivity, upwelling, and downwelling atmospheric radiances. These AFs are fitted versus the atmospheric water-vapor content for operational purposes, despite the fact that other computation options are also possible. The SC algorithm has been adapted to ASTER TIR bands 13 (10.659 ?m) and 14 (11.289 ?m), located in the typical split-window region (10.5-12 ?m), where transmission through the atmosphere is higher and surface emissivity variations are lower in comparison with the ones in the 8-9.4 ?m spectral region. Land-surface temperature retrieved with the SC algorithm has been tested over five different samples (including vegetated plots and bare soil) in an agricultural area using one single image. The comparison with ground-truth data provided a bias near to zero and standard deviations of around 2 K, with bands 13 and 14 providing similar results.

Effects of topography on the spatial distribution of evapotranspiration over a complex terrain using two‐source energy balance model with ASTER data

AbstractSpatial distribution of evapotranspiration (ET) over a complex terrain is estimated using a new approach of the conventional two‐source energy balance (TSEB) model by considering the effect of topography (difference in slope and aspect). We name this approach topography considered two‐source energy balance (T2SEB) model. The novelty of this model is the estimation of incoming shortwave solar radiation considering slope, aspect, altitude, latitude, longitude, and the day of calculation in the TSEB model, so that the new model should have wider applicability than existing models over topographically complex areas. In this study, high spatial resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data and meteorological data are used. ET over a complex terrain of Nagoya, Japan, on three different dates, 4 November 2005, 25 May 2004 and 30 October 2003, is estimated using both TSEB and T2SEB models. To validate both models, estimated results are compared with ground observation data at the flux tower site. Moreover, estimated results from TSEB and T2SEB models are compared in five different locations of different topography within the study area. Variation of net radiation absorbed by the surface (Rn) with topographical variables is also studied with the help of scatter plots. Estimated results for all three dates agreed within ±75 W m−2 with calculated values from both models at the flux tower site. TSEB underestimated/overestimated ET in sunlit/shaded areas in hilly areas. The T2SEB model estimated ET in hilly areas better than the TSEB model. Copyright © 2009 John Wiley & Sons, Ltd.

Lithological mapping in the Central Eastern Desert of Egypt using ASTER data

This study presents new methods for using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data for lithological mapping in arid environments. Visible, near-infrared and short wave infrared reflectance data have been processed and interpreted for mapping ophiolitic and granitic rocks at Fawakhir, Central Eastern Desert of Egypt. Image spectra show that the ophiolitic lithological members (serpentinites, metagabbros, and metabasalts), grey granite, and pink granite have absorption features around spectral bands 3, 6, and 8. ASTER band ratios ((2 + 4)/3, (5 + 7)/6, (7 + 9)/8) in RGB are constructed by summing the bands representing the shoulders of absorption features as a numerator, and the band located nearest the absorption feature as a denominator to discriminate between different ophiolitic and granitic rocks. The results show that ASTER band ratios ((2 + 4)/3, (5 + 7)/6, (7 + 9)/8) in a Red–Green–Blue (RGB) color combination identifies the ophiolitic rocks (serpentinites, metagabbros, and metabasalts) much better than previously published ASTER band ratios analysis. A Principal Component Analysis (PCA) was also implemented to reduce redundant information in highly correlated bands. PCA (5, 4, 2) in RGB enabled the discrimination between ophiolitic rocks and between the grey granite and pink granite. Thus, this technique is also recommended for mapping different types of granitic rocks. A new up-to-date lithologic map of the Fawakhir area is proposed based on the interpretation of ASTER image results and field verification work. It is concluded that the proposed methods have great potential for lithological mapping in arid and semi arid regions with similar climate and rock units as the Central Eastern Desert of Egypt.

Remote monitoring of tamarisk defoliation and evapotranspiration following saltcedar leaf beetle attack

Tamarisk ( Tamarix spp.) has invaded riparian ecosystems throughout the Western United States, including significant portions of riparian ecosystems within U.S. National Parks and Monuments. Recently, the saltcedar leaf beetle ( Diorhabda elongata) was released as a tamarisk biocontrol agent. Although initial releases have been monitored, no comprehensive program is currently in place to monitor the rapid spread of Diorhabda that has resulted from numerous subsequent releases by county and state agencies. Long term monitoring of tamarisk defoliation and its impacts on habitat and water resources is needed. This study examines the potential for using higher spatial resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data and lower spatial resolution Moderate Resolution Imaging Spectroradiometer (MODIS) data for monitoring defoliation caused by Diorhabda and subsequent changes in evapotranspiration (ET). Widespread tamarisk defoliation was observed in an eastern Utah study area during summer 2007. ASTER normalized difference vegetation index (NDVI) showed only minor changes between 2005 and 2006, but a significant drop in NDVI was found within riparian areas between 2006 and 2007. The decrease in NDVI caused by defoliation was apparent despite partial refoliation within the study area. MODIS time series data revealed that absolute decline in EVI varied by site, but that the timing of EVI decline during summer 2007 was early with respect to phenological patterns from 2001 through 2006. Defoliation caused decreases in ET values estimated from both ASTER and MODIS data. MODIS estimated ET declined earlier than in previous years, although annual ET was not significantly different than ET in previous years due to high year-to-year variability. Challenges to detection and monitoring of tamarisk defoliation include spectral mixing of tamarisk and other cover types at subpixel spatial resolution, spatial coregistration of time series images, the timing of image acquisition, and changes unrelated to defoliation in non-tamarisk land cover over time. Continued development of the techniques presented in this paper may allow monitoring the spread of Diorhabda and assessment of potential water salvage resulting from biocontrol of tamarisk.

Lithologic mapping using ASTER imagery and multivariate texture

Lithologic mapping using Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER) data and multivariate texture features from different wavelength regions was investigated in an area mainly composed of sedimentary rocks. Nine reflected spectral bands were used, including three visible and near-infrared (VNIR) bands and six shortwave infrared (SWIR) bands. The multivariate texture features are measured by multivariate variogram and derived from multiple bands. The obtained texture features, as additional bands, were combined with spectral data for lithologic classification, and their performances were quantitatively evaluated. The results showed that lithologic mapping using nine ASTER reflected spectral bands alone produced a relatively high overall accuracy (80.3%). However, there are still obvious confusions between different lithologic units in the classification result. Lithologic mapping by combining spectral features and textural features from VNIR or SWIR bands each produced higher accuracy than that using spectral images alone, with an approximately 7% improvement in overall accuracy and 8.5% improvement in kappa coefficient. Moreover, the combined use of these multivariate textural features from both VNIR and SWIR bands and the spectral data in lithologic classification improved the mapping results even further, with a 9.5% increase in overall accuracy and an 11.6% increase in kappa coefficient compared with those using the spectral data alone. The results demonstrated the additional discrimination capability of image texture features for lithologic identification, which significantly reduced the confusion between lithologic units with similar spectral properties but different textural features.

Performance, combustion and emissions of a diesel engine operated with reformed EGR. Comparison of diesel and GTL fuelling

In this work, the effects of a standard ultra-low sulphur diesel (ULSD) fuel and a new, ultra-clean synthetic GTL (gas-to-liquid) fuel on the performance, combustion and emissions of a single-cylinder, direct injection, diesel engine were studied under different operating conditions with addition of simulated reformer product gas, referred to as reformed EGR (REGR). For this purpose various levels of REGR of two different compositions were tested. Tests with standard EGR were also carried out for comparison. Experiments were performed at four steady state operating conditions and the brake thermal efficiency, combustion process and engine emission data are presented and discussed. In general, GTL fuel resulted in a higher brake thermal efficiency compared to ULSD but the differences depended on the engine condition and EGR/REGR level and composition. The combustion pattern was significantly modified when the REGR level was increased. Although the extent of the effects of REGR on emissions depended on the engine load, it can be generally concluded that an optimal combination of GTL and REGR significantly improved both NO x and smoke emissions. In some cases, NO x and smoke emission reductions of 75% and 60%, respectively, were achieved compared to operation with ULSD without REGR. This offers a great potential for engine manufacturers to meet the requirements of future emission regulations.

Shoreline changes and vertical displacement of the 2 April 2007 Solomon Islands earthquake Mw 8.1 revealed by ALOS PALSAR images

The Solomon Islands earthquake with magnitude Mw = 8.1 occurred on 2 April 2007 at 7:39 local time. We used six L-band Synthetic Aperture Radar (SAR) images acquired by the Advanced Land Observing Satellite (ALOS) Array L-band Synthetic Aperture Radar (PALSAR) data to roughly estimate the shoreline and vertical displacements associated with this earthquake. We processed the raw SAR data with the SIGMA-SAR software package, produced by Japan Aerospace Exploration Agency (JAXA). Our measurements showed good agreement with field observations performed by Japanese scientists just a few weeks after the earthquake. We estimated the dislocation related to this earthquake between Ranongga Island and Simbo Island. Moreover, we compared the radar imagery analysis data with Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data and found that the SAR images were more efficient for investigating vertical displacements than similar techniques based on data from optical sensors. Measurements of offset cross-correlation intensities in SAR images indicated about 1.4 m of uplift on southwestern New Georgia Island.

Expert system classification of urban land use/cover for Delhi, India

This study presents the results of classifying land use/land cover for Delhi, India using an expert system approach. For this study Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data of 22 September 2003 were used. The research goals of this project are two‐fold. In one respect, the research goal is to report on the extent covered by urbanization using the classified image. Thirteen different land‐cover categories were identified with an 85.55% overall classification accuracy based on 256 random points for validation and 50 on the ground observations. Secondly, we report on our efforts to duplicate an expert system model previously developed for Phoenix Arizona as a generalized approach for urban land use classification. Results suggest that while some of the methodology could be duplicated, there are local factors (e.g. data availability and specific land features) that required the approach to be modified.

Mapping mineralogical alteration using principal‐component analysis and matched filter processing in the Takab area, north‐west Iran, from ASTER data

The Takab area, located in north‐west Iran, is an important gold mineralized region with a long history of gold mining. The gold is associated with toxic metals/metalloids. In this study, Advanced Space Borne Thermal Emission and Reflection Radiometer data are evaluated for mapping gold and base‐metal mineralization through alteration mapping. Two different methods are used for argillic and silicic alteration mapping: selective principal‐component analysis and matched filter processing (MF). Running a selective principal‐component analysis using the main spectral characteristics of key alteration minerals enhanced the altered areas in PC2. MF using spectral library and laboratory spectra of the study area samples gave similar results. However, MF, using the image reference spectra from principal component (PC) images, produced the best results and indicated the advantage of using image spectra rather than library spectra in spectral mapping techniques. It seems that argillic alteration is more effective than silicic alteration for exploration purposes. It is suggested that alteration mapping can also be used to delineate areas contaminated by potentially toxic metals.

A Hybrid Remote Sensing Approach to Quantifying Crop Residue Burning in the United States

Crop residue burning is an important land use activity in the United States. Currently, satellite-based burned area methodologies specifically calibrated for crop residue burning are limited. This article describes a satellite observations-based hybrid approach to estimate the amount of burned crop residues that combines Moderate Resolution Imaging Spectroradiometer (MODIS) 8-day differencing of Normalized Burn Ratio (dNBR) burned area mapping with MODIS active fire counts calibrated into area. The dNBR approach utilizes the spectral response of the 2.1-µm shortwave infrared MODIS band to detect burned pixels. A time series of 8-day MODIS composites produces burned area estimates during harvest on a near-weekly scale. This approach was tested on the study area of MODIS tile h10v05, which encompasses much of the Mississippi River Delta and the southern Great Plains, for the years 2003 through 2006. Within this area, an average of 12,700 and 10,835 km2 burned in the spring and fall harvests, respectively. Results from the hybrid approach are validated through comparison with high-resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data and field data. Validation of the hybrid approach shows strong correspondence with both the ASTER (mean R2 = 0.92) and in-situ data (mean accuracy 85.5%). At the state level, the estimated burn rates from this analysis compare well with reported Arkansas burn rates. Results suggest potential for using the approach to monitor and quantify fire activity in cropland areas of the United States.

Identification of quartz and carbonate minerals across northern Nevada using ASTER thermal infrared emissivity data—Implications for geologic mapping and mineral resource investigations in well-studied and frontier areas

ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) thermal infrared imagery over a 389 km × 387 km area in northern Nevada (38.5°–42°N, 114°–118.5°W) was analyzed to evaluate its capability for accurate and cost-effective identification and mapping of quartz and carbonate minerals at regional to local scales. The geology of this area has been mapped at a wide range of scales and includes a diversity of rock types and unconsolidated surficial materials, many of which are composed primarily of quartz and carbonate minerals. This area is also endowed with a wide variety of economically and scientifically important ore deposit types that contain an array of commodities (Au, Ag, Pb, Zn, Cu, Mo, W, Sn, Be, F, Mn, Fe, Sb, Hg, and barite). The hydrothermal systems that generated these deposits frequently deposited large amounts of quartz where fluids cool, and generally smaller amounts of calcite or dolomite by other mechanisms. To identify and map quartz and carbonate minerals, band ratioing techniques were developed based on the shapes of laboratory reference spectra and applied to ASTER Level 2 surface emissivity products of 108 overlapping scenes. These mineral maps were mosaicked into a single coverage that was overlain with published, vector-format geologic maps of various scales to determine which geologic terranes, formations, and geomorphic features correspond to identified quartz or carbonate. Where quartz or carbonate minerals were mapped in rocks composed primarily of other minerals, they were inferred to be hydrothermal in origin and compared to known occurrences of hydrothermal alteration and mineralization. The ASTER-based quartz mapping identified thick sequences of quartzite, bedded radiolarian chert, quartz sandstone, conglomerates with clasts of quartzite and chert, silicic and/or altered rhyolites, and silicic welded tuffs. Alluvial fan surfaces, sand dunes, and beach deposits composed of quartz and/or carbonate are prominent, well-mapped features. Quartz was also identified in smaller bodies of jasperoid, quartz-alunite, and quartz-sericite-pyrite alteration, hot spring silica sinter terraces, and several diatomite and perlite mines and prospects. The ASTER-based carbonate mapping identified thick sequences of dolomite, limestone, and marble, as well as small hot spring travertine deposits. Eolian carbonate was identified in several playas. Dolomite exhibited a stronger carbonate response than calcite, as predicted based on their thermal spectral characteristics. Quartz was detected at lower concentrations than carbonates because of the greater strength of the quartz reststrahlen features in the thermal infrared compared to the bending-related spectral features of carbonates. The 90 m ground pixel size of the ASTER thermal imagery prevents the identification of small-scale features. Despite this limitation, numerous bodies of hydrothermal quartz were detected in or near known Carlin-type gold deposits, distal disseminated Au-Ag deposits, high- and low-sulfidation epithermal Au-Ag deposits, and geothermal areas. Detection of hydrothermal carbonate was rare and mainly in geothermal areas. The ASTER-based thermal quartz and carbonate mapping demonstrated here can be used in well-studied or frontier areas to verify the accuracy of existing geologic maps, guide future detailed stratigraphic and structural mapping in lithologically complex terranes and allochthons, and identify hydrothermal features for exploration and resource assessment purposes.

Mapping evapotranspiration in the Indus Basin using ASTER data

Conventional methods that use point measurements to estimate evapotranspiration are representative only of local areas and cannot be extended to large areas because of heterogeneity of landscape. To overcome this difficulty, remote sensing has proven to be the most suitable approach for large area estimation of evapotranspiration because remote sensing data can provide representative parameters such as radiometric surface temperature, albedo and vegetation index. The heterogeneity is more prominent in the Indus Basin as more than 80% of farmers have land holdings less than 4 ha, and within these holdings, two or three different crops are usually grown. The limitation of most remote sensing based procedures to estimate evapotranspiration is the measurements of large number of crop‐specific and climatic parameters, which are not only difficult to obtain but also require considerable field work, equipment and therefore involve much expenditure. The purpose of this study was to present a simple methodology that requires minimum ground observations for estimation of evapotranspiration to test the reliability of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data for estimation of evapotranspiration in the Indus Basin. The methodology is based on surface energy balance to estimate sensible and latent heat fluxes by combining remotely sensed data from ASTER with common meteorological data. The various components of surface energy balance were computed during satellite overpass and 24‐h integrated fluxes were derived for the full ASTER scene acquired over the lower Rechna doab region of the Indus Basin. The surface brightness temperatures were derived from thermal band 13 and NDVI from two VNIR bands of the ASTER. Evapotranspiration values from the maize field in the Indus Basin, as estimated using ASTER data at Shahkot, Jaranwala and Satiana locations, were estimated as 2.05, 2.77 and 2.32 mm day−1, respectively. The estimated evapotranspiration was compared with evapotranspiration computed at three different locations using CROPWAT software and was found to be in close agreement.

Automatic mapping of snow cover depletion curves using optical remote sensing data under conditions of frequent cloud cover and temporary snow

AbstractSnow cover depletion curves are required for several water management applications of snow hydrology and are often difficult to obtain automatically using optical remote sensing data owing to both frequent cloud cover and temporary snow cover. This study develops a methodology to produce accurate snow cover depletion curves automatically using high temporal resolution optical remote sensing data (e.g. Terra Moderate Resolution Imaging Spectroradiometer (MODIS), Aqua MODIS or National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR)) by snow cover change trajectory analysis. The method consists of four major steps. The first is to reclassify both cloud‐obscured land and snow into more distinct subclasses and to determine their snow cover status (seasonal snow cover or not) based on the snow cover change trajectories over the whole snowmelt season. The second step is to derive rules based on the analysis of snow cover change trajectories. These rules are subsequently used to determine for a given date, the snow cover status of a pixel based on snow cover maps from the beginning of the snowmelt season to that given date. The third step is to apply a decision‐tree‐like processing flow based on these rules to determine the snow cover status of a pixel for a given date and to create daily seasonal snow cover maps. The final step is to produce snow cover depletion curves using these maps. A case study using this method based on Terra MODIS snow cover map products (MOD10A1) was conducted in the lower and middle reaches of the Kaidu River Watershed (19 000 km2) in the Chinese Tien Shan, Xinjiang Uygur Autonomous Region, China. High resolution remote sensing data (charge coupled device (CCD) camera data with 19·5 m resolution of the China and Brazil Environmental and Resources Satellite (CBERS) data (19·5 m resolution), and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data with 15 m resolution of the Terra) were used to validate the results. The study shows that the seasonal snow cover classification was consistent with that determined using a high spatial resolution dataset, with an accuracy of 87–91%. The snow cover depletion curves clearly reflected the impact of the variation of temperature and the appearance of temporary snow cover on seasonal snow cover. The findings from this case study suggest that the approach is successful in generating accurate snow cover depletion curves automatically under conditions of frequent cloud cover and temporary snow cover using high temporal resolution optical remote sensing data. Copyright © 2007 John Wiley & Sons, Ltd.

Plagioclase compositions derived from thermal emission spectra of compositionally complex mixtures: Implications for Martian feldspar mineralogy

The compositions of plagioclase, the most abundant mineral in the Martian crust, reflect changing conditions during magmatic evolution. Plagioclase contains spectral features at thermal infrared wavelengths that permit its detection by thermal emission spectrometers (Thermal Emission Spectrometer (TES), Thermal Emission Imaging System (THEMIS), and Miniature TES (Mini‐TES)) on Mars spacecraft. Previous studies have determined the accuracy with which average plagioclase compositions can be modeled in simple two‐component sand mixtures and terrestrial volcanic rocks. Studies of terrestrial rock analogs suffer from difficulties in accurately determining the average plagioclase composition for comparison with the spectrally modeled composition. Sand mixtures, however, provide a means of controlling plagioclase compositions for direct comparison to those modeled by linear deconvolution. This has allowed us to address how compositional complexity may affect our ability to derive average plagioclase compositions from thermal emission data. In this study, we examine the accuracy with which average plagioclase compositions can be modeled from emission spectra of complex mixtures of three, four, and five compositions of coarse (500–850 μm) plagioclase sand. Additionally, we examine multiphase mixtures of plagioclase with pyroxene, olivine, magnetite, and ilmenite that are analogous to selected Martian surface materials. Increasing the number of plagioclase compositions or introducing additional mineral phases does not affect the accuracy previously reported for modeling average plagioclase compositions. Plagioclase can be modeled to within 6 An of measured compositions at laboratory, TES, THEMIS, and Mini‐TES resolution (within 1σ standard deviation).