Showing papers in "Remote Sensing in 2004"

Fully automated analysis of space-based lidar data: an overview of the CALIPSO retrieval algorithms and data products

Abstract: The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite will be launched in April of 2005, and will make continuous measurements of the Earth's atmosphere for the following three years. Retrieving the spatial and optical properties of clouds and aerosols from the CALIPSO lidar backscatter data will be confronted by a number of difficulties that are not faced in the analysis of ground-based data. Among these are the very large distance from the target, the high speed at which the satellite traverses the ground track, and the ensuing low signal-to-noise ratios that result from the mass and power restrictions imposed on space-based platforms. In this work we describe an integrated analysis scheme that employs a nested, multi-grid averaging technique designed to optimize tradeoffs between spatial resolution and signal-to-noise ratio. We present an overview of the three fundamental retrieval algorithms (boundary location, feature classification, and optical properties analysis), and illustrate their interconnections using data product examples that include feature top and base altitudes, feature type (i.e., cloud or aerosol), and layer optical depths.

MODTRAN5: a reformulated atmospheric band model with auxiliary species and practical multiple scattering options

Abstract: The MODTRAN5(1a, in press) radiation transport (RT) model is a major advancement over earlier versions of the MODTRAN(tm) atmospheric transmittance and radiance model. New model features include (1) finer spectral resolution via the Spectrally Enhanced Resolution MODTRAN(tm) (SERTRAN) molecular band model, (2) a fully coupled treatment of auxiliary molecular species, and (3) a rapid, high fidelity multiple scattering (MS) option. The finer spectral resolution improves model accuracy especially in the mid- and long-wave infrared atmospheric windows; the auxiliary species option permits the addition of any or all of the suite of HITRAN molecular line species, along with default and user-defined profile specification; and the MS option makes feasible the calculation of Vis-NIR databases that include high-fidelity scattered radiances.

Status and performance of the CALIOP lidar

Abstract: The Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP) is the primary instrument on the CALIPSO satellite, which is scheduled to launch in 2005. CALIOP will provide profiles of total backscatter at two wavelengths, from which aerosol and cloud profiles will be derived. The instrument also measures the linear depolarization of the backscattered return, allowing discrimination of cloud phase and the identification of the presence of non-spherical aerosols. CALIOP is complete and has been tested in a ground-based configuration. This paper provides information on basic characteristics and performance of CALIOP.

Spectral characteristics preserving image fusion based on Fourier domain filtering

Abstract: Data fusion methods are usually classified into three levels: pixel level (ikonic), feature level (symbolic) and knowledge or decision level Here, we will focus on the development of ikonic techniques for image fusion Image transforms such as the Intensity-Hue-Saturation (IHS) or Principal Component (PC) transform are widely used to fuse panchromatic images of high spatial resolution with multispectral images of lower resolution These techniques create multispectral images of higher spatial resolution but usually at the cost that these transforms do not preserve the original color or spectral characteristics of the input image data In this study, a new method for image fusion will be presented that is based on filtering in the Fourier domain This method preserves the spectral characteristics of the lower resolution mul-tispectral images Examples are presented for SPOT and Ikonos panchromatic images fused with Landsat TM and Iko-nos multispectral data Comparison with existing fusion techniques such as IHS, PC or Brovey transform prove the su-periority of the new method While in principle based on the IHS transform (which usually only works for three bands), the method is extended to any arbitrary number of spectral bands Using this approach, this method can be applied to sharpen hyperspectral images without changing their spectral behavior

Lithologic mapping with multispectral ASTER TIR and SWIR data

Abstract: ASTER, launched in December, 1999, composed of three subsystems, each of which multispectrally observes the reflected or emitted radiation from the surface of the earth to space in VNIR (visible and near infrared), SWIR (shortwave infrared) and TIR (thermal infrared) wavelength regions, respectively. ASTER-VNIR has three spectral bands with a spatial resolution of 15m, and the one of which in near infrared has an along track stereo observation capability to produce high quality Digital Elevation Model (DEM). ASTER-SWIR has six spectral bands with a spatial resolution of 30m, which are mainly designed for discriminating altered minerals bearing hydroxyl group. ASTER-TIR has five spectral bands with a spatial resolution of 90m, which presents us a powerful tool for identifying quartz and carbonate minerals as well as discriminating types of silicate rocks. The author have successfully developed a robust method for detecting quartzite and carbonate rocks as well as classifying type of igneous rocks with ASTER TIR data without atmospheric corrections (Level-1B data). Here in this paper, reflectance spectra of minerals in SWIR region measured in the laboratory are analyzed to define calcite index, OH-bearing silicate index, kaolinite index and alunite index for discriminating each mineral by ASTER-SWIR. The defined indices are applied to SWIR data of ASTER Level-1B radiance at the sensor data observing Cuprite area in Nevada, USA, and the discussions are made on the results by comparing the well-known geology of the area. Also, the result of calcite index is compared with the result of applying well-characterized carbonate index defined for ASTER-TIR to clarify the strong point of each index.

CERES cloud property retrievals from imagers on TRMM, Terra, and Aqua

Abstract: The micro- and macrophysical properties of clouds play a crucial role in Earth’s radiation budget The NASA Clouds and Earth’s Radiant Energy System (CERES) is providing simultaneous measurements of the radiation and cloud fields on a global basis to improve the understanding and modeling of the interaction between clouds and radiation at the top of the atmosphere, at the surface, and within the atmosphere Cl oud properties derived for CERES from the Moderate Resolution Imaging Spectrora diometer (MODIS) on the Terra and Aqua satellites are compared to ensure consistency between the products to ensure the reliability of the retrievals from multiple platforms at different times of day Comparisons of cloud fraction, height, optical depth, phase, effective particle size, and ice and liquid water paths from the two satellites show excellent consistency Initial calibration comparisons are also very favorable Differences between the Aqua and Terra results are generally due to diurnally dependent changes in the clouds Additional algorithm refinement is needed over the polar regions for Aqua and at night over those same areas for Terra The results should be extremely valuable for model validation and improvement and for improving our understanding of the relationship between clouds and the radiation budget keywords: radiation, clouds, remote sensing, cloud microphysics, climatology, MODIS, CERES, VIRS, Aqua, Terra

TerraSAR-X mission

Abstract: The TerraSAR-X is a German national SAR- satellite system for scientific and commercial applications. It is the continuation of the scientifically and technologically successful radar missions X-SAR (1994) and SRTM (2000) and will bring the national technology developments DESA and TOPAS into operational use. The space segment of TerraSAR-X is an advanced high-resolution X-Band radar satellite. The system design is based on a sound market analysis performed by Infoterra. The TerraSAR-X features an advanced high-resolution X-Band Synthetic Aperture Radar based on the active phased array technology which allows the operation in Spotlight-, Stripmap- and ScanSAR Mode with various polarizations. It combines the ability to acquire high resolution images for detailed analysis as well as wide swath images for overview applications. In addition, experimental modes like the Dual Receive Antenna Mode allow for full-polarimetric imaging as well as along track interferometry, i.e. moving target identification. The Ground Segment is optimized for flexible response to (scientific and commercial) User requests and fast image product turn-around times. The TerraSAR-X mission will serve two main goals. The first goal is to provide the strongly supportive scientific community with multi-mode X-Band SAR data. The broad spectrum of scientific application areas include Hydrology, Geology, Climatology, Oceanography, Environmental Monitoring and Disaster Monitoring as well as Cartography (DEM Generation) and Interferometry. The second goal is the establishment of a commercial EO-market in Europe which is driven by Infoterra. The commercial goal is the development of a sustainable EO-business so that the e.g. follow-on systems can be completely financed by industry from the profit. Due to its commercial potential, the TerraSAR-X project will be implemented based on a public-private partnership with the Astrium GmbH. This paper will describe first the mission objectives as well as the project organisation and major milestones. Then an overview on the satellite as well as the SAR instrument is given followed by a description of the system design. Finally the principle layout of the TerraSAR-X Ground Segment and some remarks on the European context are presented.

Retrieval of CH 4 , CO, and CO 2 total column amounts from SCIAMACHY near-infrared nadir spectra: retrieval algorithm and first results

Abstract: SCIAMACHY is a UV/visible/near-infrared grating spectrometer on board the European environmental satellite ENVISAT that observes the atmosphere in nadir, limb, and solar and lunar occultation viewing geometries with moderate spectral resolution (0.2-1.5 nm). At the University of Bremen a modified DOAS algorithm (WFM-DOAS) is being developed primarily for the retrieval of CH4, CO, CO2, H2O, N2O, and O2 total columns from SCIAMACHY near-infrared and visible nadir spectra. A first version of this algorithm has been implemented based on a fast look-up table approach. The algorithm and the look-up table is described along with an initial error analysis. Weighting functions and averaging kernels indicate that the SCIAMACHY near-infrared nadir measurements are highly sensitive to trace gas concentration changes even in the lowest kilometer of the atmosphere. The results presented have been obtained by applying WFM-DOAS to small spectral fitting windows focusing on CH4, CO2, CO, and O2 column retrieval and CH4 and CO2 to O2 column ratios (denoted XCH4 and XCO2, respectively). These type of data products are planned to be used within the EU research project EVERGREEN to constrain surface sources and sinks of CH4 and CO2 using inverse modeling techniques. This study discussed the first set of WFM-DOAS products generated for and to be further improved within EVERGREEN. Although no detailed validation has been performed yet we found that the retrieved columns have the right order of magnitude and show (at least qualitatively) the expected correlation of the well mixed gases CO2 and CH4 with O2 and surface topography. The standard deviation of the dry air column averaged mixing ration XCO2 within 10° latitude bands is ±10 ppmv or 2.7% (XCH4: ±50 ppbv or ±2.8%) for measurements over land (over ocean the scatter is a factor of 2-4 larger). These values have been determined from ~25% of the ground pixels of one orbit which fulfill the following requirements: (nearly) cloud free, solar zenith angle <75°, XCO2 error < 4% (XCH4 error < 6%). It has not been assessed how much of this variability can be attricuted to real column changes. The observed variability is about three times larger than expected from (single spectra) signal-to-noise considerations but might be affected by limitations of the current implementation of the retrieval algorithm (e.g., sensitivity to surface reflectivity) and calibrations issues (e.g., not yet considered ADC non-linearity correction). Especially the CO retrieval needs further study and improvement. The CO fit errors are 20-40% over land but typically significantly larger over the ocean. A clear identification of the weak CO lines is difficult as the CO fit residuals are dominated by relatively stable systematic artifacts (also observed in the CO2 and CH4 fitting windows) on the order of the weak CO absorption lines. This might be explained by the still preliminary calibration of the SCIAMACHY spectra and/or errors of the spectroscopic data.

Mapping imperviousness using NDVI and linear spectral unmixing of ASTER data in the Cologne-Bonn region (Germany)

Abstract: Information about imperviousness surface distributions is essential for several environmental applications and the planning and management of sustainable development of urban areas Satellite remote sensing based mapping of imperviousness has shown important potentials to acquire such information in great spatial detail but the actual mapping process has been challenged by the heterogeneity of urban environment and limited spatial and spectral sensor capabilities This study explores and compares two methods based on the vegetation fraction from linear spectral unmixing and the NDVI to map the degree of imperviousness in the urban agglomeration of Cologne/Bonn in Western Germany The study employed data from the ASTER satellite sensor with improved spatial and spectral resolution Fieldwork was carried out in the area of Bonn to obtain a comprehensive set of reference data with estimated degrees of imperviousness for different types of urban areas Rural areas were excluded using data from the governmental land information system (ATKIS) The applied simple linear spectral unmixing approach revealed less suitable results for the built area fraction due to the heterogeneity of the spectral response from urban targets The vegetation fraction and the NDVI provided sufficient results in estimating the impervious surface fraction that were used to derive related maps for the study areas

Determination of mixing layer heights from ceilometer data

Abstract: The Vaisala ceilometer LD40 is an eye-safe commercial lidar. It is designed originally to detect cloud base heights and vertical visibility for aviation safety purposes. The instrument was operated continuously at different measurement campaigns to detect mixing layer height from aerosol backscatter profiles. First results with the CT25K ceilometer were presented last year in the paper SPIE 5235-64 from the environmental measuring campaign in the frame of the BMBF-funded project VALIUM in Hanover, Germany, investigating the air pollution in a street canyon and the surrounding with various sensors. A software for routine retrieval of mixing layer height (MLH) from ceilometer data was developed. A comparison with mixing layer height retrievals from a SODAR and a wind-temperature-radar (WTR) operated in the urban region of Munich will be shown. The three instruments give information that partly agree and partly complement each other. The ceilometer gives information on the aerosol content of the air and the WTR provides a direct measurement of the vertical temperature distribution in the boundary layer. The WTR and the ceilometer add information on the moisture structure of the boundary layer that is not detected by the SODAR which gives information on the thermal structure. On the other hand this comparison validates known techniques by which the MLH is derived from SODAR data. In the absence of low clouds and precipitation ceilometers can estimate the mixing-layer-height fairly well. The potential of the ceilometer, being the smallest instrument among the used ones as LIDAR, SODAR and WTR, will be discussed to be used in future MLH studies.

Performance of satellite-to-ground communications link between ARTEMIS and the Optical Ground Station

Abstract: The European Space Agency has built an optical ground station sited at the Observatorio del Teide operated by the Instituto de Astrofisica de Canarias. This station, equipped with a 1m telescope, has a multipurpose configuration for in-orbit commissioning and checkout of laser communication payloads. Since November 2001, the bidirectional link with satellite ARTEMIS has been established in more than 80 successful sessions. In this paper, we analyze the influence of turbulence parameters on the performance of communications in the bidirectional ground to space laser communication experiments. The link performance observed in the satellite-to-ground channel showed average bit error rates of 1E-6 over long durations (20 minutes), however in some occasions BER's of at least 10-9 -10-10 over durations of 5 to 30 minutes were observed. The behavior of the Bit Error Rate measurements performed in different turbulence conditions is characterized.

Comparison of very high spatial resolution satellite image segmentations

Abstract: Since 1999, very high spatial resolution data represent the surface of the earth with more details. However, information extraction by computer-assisted classification techniques proves to be very complex owing to the internal variability increase in land-cover units and to the weakness of spectral resolution. The increase in variability decreases the statistical separability of land-cover classes in the spectral space. Per pixel multispectral classification techniques are then insufficient for an extraction of complex categories and spectrally heterogeneous land-cover, like urban areas. Per region classification was proposed as an alternative approach. The first step of this approach is the segmentation. A large variety of segmentation algorithms were developed these last 20 years and a comparison of their implementation on very high spatial resolution images is necessary. For this study, four algorithms from the two main groups of segmentation algorithms (boundary-based and region-based algorithms) were selected. In order to compare the algorithms, an evaluation of each algorithm was carried out with empirical discrepancy evaluation methods. This evaluation is carried out with a visual segmentation of IKONOS panchromatic images.

Studies of pointing, acquisition, and tracking of agile optical wireless transceivers for free-space optical communication networks

Abstract: Free space, dynamic, optical wireless communications will require topology control for optimization of network performance. Such networks may need to be configured for bi- or multiple-connectedness, reliability and quality-of-service. Topology control involves the introduction of new links and/or nodes into the network to achieve such performance objectives through autonomous reconfiguration as well as precise pointing, acquisition, tracking, and steering of laser beams. Reconfiguration may be required because of link degradation resulting from obscuration or node loss. As a result, the optical transceivers may need to be re-directed to new or existing nodes within the network and tracked on moving nodes. The redirection of transceivers may require operation over a whole sphere, so that small-angle beam steering techniques cannot be applied. In this context, we are studying the performance of optical wireless links using lightweight, bi-static transceivers mounted on high-performance stepping motor driven stages. These motors provide an angular resolution of 0.00072 degree at up to 80,000 steps per second. This paper focuses on the performance characteristics of these agile transceivers for pointing, acquisition, and tracking (PAT), including the influence of acceleration/deceleration time, motor angular speed, and angular re-adjustment, on latency and packet loss in small free space optical (FSO) wireless test networks.

New optical concept for commercial lidar ceilometers scanning the boundary layer

Abstract: The sensitivity of commercial lidar ceilometers for detecting aerosols within the boundary layer is sufficient to give reliable information on parameters like the mixing layer height. The traditional optical concepts of these lidars are either biaxial two-lens systems or one-lens systems with separate compensation techniques for the internal optical cross talk. The single lens concept is superior to the biaxial system when reliable data from the near range up to 300 m elevation is required. This paper introduces an enhanced single lens system removing the internal optical cross-talk between the laser transmitter and the receiver. The new Vaisala Ceilometer CL31 uses this optical layout to improve cloud and vertical visibility detection performance in precipitation, fog and haze situations. On the other hand it also provides advanced boundary layer scans during clear sky weather. Such scans are performed around the clock in the Vaisala test field by ceilometers using the three optical systems discussed. A comparison of cases covering a variety of different meteorological situations illustrates the advantages of the new optical concept. Mixing layer height values are determined with a gradient method and compared to radio sounding data.

Mapping of submerged aquatic vegetation with a physically based process chain

Abstract: Mapping the submerse vegetation is of prime importance for the ecological evaluation of an entire lake. Remote sensing techniques are efficient for such mapping tasks, if the retrieval algorithms and processing methods are robust and mostly independent from additional ground truth measurements. The Modular Inversion Program (MIP) follows this concept. It is a processing tool designed for the recovery of hydro-biological parameters from multi- and hyper-spectral remote sensing data. The architecture of the program consists of physical inversion schemes that derive bio-physical parameters from the measured radiance signal at the sensor. Program modules exist for the retrieval of aerosols, sun glitter correction, atmospheric corrections, retrieval of water constituents among others. For the purpose of mapping the bottom coverage in optically shallow waters, two modules have been added to MIP. The first module calculates the bottom reflectance using the subsurface reflectance, the depth and an approximation of the water constituent concentrations as input. The second module fractionalizes the bottom reflectance to three endmembers of specific reflectance spectra by linear unmixing. The three endmembers are specific reflectance spectra of bottom sediments, small growing macrophytes (Characeae) and tall macrophytes such as Potamogeton perfoliatus & P. pectinatus. The processing system has been tested with data collected from the multi-spectral airborne scanner Daedalus AADS1268 at Lake Constance, Germany, for multi- temporal analysis.

ASTER/TIR onboard calibration status and user-based recalibration

Abstract: Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), one of five sensors on Terra, has five bands (10 to 14) in the thermal infrared (TIR) region. These TIR bands are radiometrically calibrated by one onboard blackbody with the function of changing temperature between 270 and 340 K. In normal operation the blackbody is set up at 270 K, and a constant coefficient in a quadratic radiometric calibration equation for each detector is adjusted at that temperature before each Earth observation, but the gain coefficient cannot be adjusted at this time, while it can periodically be updated by long term calibration in which the blackbody is measured at 270, 300, 320, and 340 K. On the other hand the sensor response of all bands (particularly band 12) has been degrading since the launch, and periodical updating of the gain coefficient does not fully follow the degradation, so that the calibration error on level-1 (L1) products is often unacceptable. We therefore have developed a recalibration method which is easily applied to L1 products by a general user. By using this method, the calibration error will mostly be reduced below the level of NEDT.

Using the moon for MODIS on-orbit spatial characterization

Abstract: The moon is a very stable reference source that has been used for the space-borne sensors’ radiometric calibration and/or radiometric stability monitoring. In this paper, we present an approach that uses the sensors’ on-orbit lunar observations for their spatial characterization and apply the method to the MODIS instruments that are currently operating on board NASA EOS Terra and Aqua satellites. Both MODIS instruments perform monthly lunar observations. The spatial characterization results derived from the lunar observations using this algorithm are compared with those obtained from the MODIS Spectro-Radiometric Calibration Assembly (SRCA), which is an on-board calibrator capable of performing spatial characterizations for all MODIS spectral bands. The new approach can be applied to other remote sensing instruments.

MODIS correction algorithm for out-of-band response in the short-wave IR bands

Abstract: The MODerate Resolution Imaging Spectroradiometer (MODIS) has 36 spectral bands with wavelengths from 0.41 to 14.5 micrometers. The 36 spectral bands, with a total of 490 detectors, are distributed on four focal plane assemblies (FPAs): visible (VIS), near infrared (NIR), short- mid-wave infrared (SMIR), and long wave infrared (LWIR). Nearly identical copies of the MODIS are currently operating onboard the NASA EOS Terra (launched on December 18,1999) and Aqua spacecraft (launched on May 4, 2002). Prelaunch and on-orbit characterizations of both Terra and Aqua MODIS have shown small but non-negligible out-of-band (OOB) response in the sensor's short-wave infrared bands (SWIR): bands 5-7, and band 26. To minimize the impact due to OOB response on the MODIS SWIR bands calibration and the Earth scene product retrieval, an algorithm has been developed and implemented in the Level 1B (L1B) software for both Terra and Aqua MODIS. In this paper, we describe the algorithm and its applications to the MODIS L1B calibration algorithms. We illustrate how the correction coefficients are derived from on-orbit observations and discuss the test procedures involved before the final implementation in the L1B code. Performance is evaluated for both Terra and Aqua MODIS and the two results are compared.

Reconfigurable optical wireless sensor networks

Abstract: Optical wireless networks are emerging as a viable, cost effective technology for rapidly deployable broadband sensor communication infrastructures. The use of directional, narrow beam, optical wireless links provides great promise for secure, extremely high data rate communication between fixed or mobile nodes, very suitable for sensor networks in civil and military contexts. The main challenge is to maintain the quality of such networks, as changing atmospheric and platform conditions critically affect their performance. Topology control is used as the means to achieve survivable optical wireless networking under adverse conditions, based on dynamic and autonomous topology reconfiguration. The topology control process involves tracking and acquisition of nodes, assessment of link-state information, collection and distribution of topology data, and the algorithmic solution of an optimal topology. This paper focuses on the analysis, implementation and evaluation of algorithms and heuristics for selecting the best possible topology in order to optimize a given performance objective while satisfying connectivity constraints. The work done at the physical layer is based on link cost information. A cost measure is defined in terms of bit-error-rate and the heuristics developed seek to form a bi-connected topology which minimizes total network cost. At the network layer a key factor is the traffic matrix, and heuristics were developed in order to minimize congestion, flow-rate or end-to-end delay.

APEX; current status of the airborne dispersive pushbroom imaging spectrometer

Abstract: Recently, a joint Swiss/Belgian initiative started a project to build a new generation airborne imaging spectrometer, namely APEX (Airborne Prism Experiment) under the ESA funding scheme named PRODEX. APEX is a dispersive pushbroom imaging spectrometer operating in the spectral range between 380 - 2500 nm. The spectral resolution will be better then 10 nm in the SWIR and < 5 nm in the VNIR range of the solar reflected range of the spectrum. The total FOV will be ± 14 deg, recording 1000 pixels across track with max. 300 spectral bands simultaneously. APEX is subdivided into an industrial team responsible for the optical instrument, the calibration homebase, and the detectors, and a science and operational team, responsible for the processing and archiving of the imaging spectrometer data, as well as for its operation. APEX is in its design phase and the instrument will be operationally available to the user community in the year 2006.

Non-mechanical zoom system

Abstract: In order to optically vary the magnification of an imaging system, mechanical zoom lenses, such as those found on 35mm cameras, require multiple optical elements and use cams or gears to adjust the spacing between individual or groups of lenses. By incorporating active elements in the optical design, we can eliminate the need to change lens separations and create an imaging system with variable optical magnification that has no macroscopic moving parts.

Aerosol models for the CALIPSO lidar inversion algorithms

Abstract: We use measurements and models to develop aerosol models for use in the inversion algorithms for the Cloud Aerosol Lidar and Imager Pathfinder Spaceborne Observations (CALIPSO). Radiance measurements and inversions of the AErosol RObotic NETwork (AERONET) are used to group global atmospheric aerosols using optical and microphysical parameters. This study uses more than 105 records of radiance measurements, aerosol size distributions, and complex refractive indices to generate the optical properties of the aerosol at more 200 sites worldwide. These properties together with the radiance measurements are then classified using classical clustering methods to group the sites according to the type of aerosol with the greatest frequency of occurrence at each site. Six significant clusters are identified: desert dust, biomass burning, urban industrial pollution, rural background, marine, and dirty pollution. Three of these are used in the CALIPSO aerosol models to characterize desert dust, biomass burning, and polluted continental aerosols. The CALIPSO aerosol model also uses the coarse mode of desert dust and the fine mode of biomass burning to build a polluted dust model. For marine aerosol, the CALIPSO aerosol model uses measurements from the SEAS experiment. In addition to categorizing the aerosol types, the cluster analysis provides all the column optical and microphysical properties for each cluster.

Aerosol concentration measurements with a lidar ceilometer: results of a one year measuring campaign

Abstract: The Vaisala ceilometer CT25K is an eye-safe commercial lidar mainly used to report cloud base heights and vertical visibility for aviation safety purposes. Compared to ceilometers with biaxial optics, its single lens design provides a higher signal-to-noise ratio for lidar return signals from distances below about 600 m, thus increasing its abilities to examine the mixing layer. A CT25K ceilometer took part in the environmental research project VALIUM at the Lower Saxony State Agency for Ecology (NLO) in Hannover, Germany, investigating the air pollution in an urban surrounding with various sensors. Lidar return signals are reported every 15 s with a height resolution of 15 m. This paper covers two aspects of the interpretation of these signals. The aerosol backscatter of the atmosphere up to 30 m is compared to the PM10 concentration reported by an in situ sensor every 30 minutes, and the results are interpreted in respect of meteorological parameters such as humidity, temperature, wind, and global radiation. With relative humidity values below 62 % and no rain present the correlation between ceilometer backscatter and PM10 values is good enough to qualify standard ceilometers as instruments for a quantitative analysis of the atmospheric aerosol contents. Backscatter values up to 1000 m height are presented that allow an estimation of the convective boundary layer top in dry weather situations. The atmospheric boundary layer structures derived from ceilometer data are compared to those reported by a SODAR and a RASS that also took part in the VALIUM research project. Finally the backscatter data quality of a double lens ceilometer is compared to that of the single lens CT25K ceilometer to investigate to what extent these lidar systems are also able to report aerosol concentration.

On the darkest pixel atmospheric correction algorithm: a revised procedure applied over satellite remotely sensed images intended for environmental applications

Abstract: Atmospheric correction is an essential part of the pre-processing of satellite remote sensing data. Several atmospheric correction approaches can be found in the literature ranging from simple to sophisticated methods. The sophisticated methods require auxiliary data, however the simple methods are based only on the image itself and are served to be suitable for operational use. One of the most widely used and well-known simple atmospheric correction methods is the darkest pixel (DP). Despite of its simplicity, the user must be aware of several key points in order to avoid any erroneous results. Indeed, this paper addresses a new strategy for selecting the suitable dark object based on the proposed analysis of digital number histograms and image examination. Several case studies, in which satellite remotely sensed image data intended for environmental applications have been atmospherically corrected using the DP method, are presented in this article.

Fast MTF measurement of CMOS imagers at the chip level using ISO 12233 slanted-edge methodology

Abstract: MTF measurement methods for imaging devices usually require the use of an optical system to project the image of the object onto the detector. So, MTF results quality strongly depends on the accuracy of the optical adjustments (alignments, focusing...). Dedicated edge patterns have been implemented at the chip level on a CMOS imager. One of them emulates the target used in the ISO 12233 slanted-edge technique and the others one are inspired by the knife-edge method. This allows to get the MTF data without optical focusing. In order to validate the results, comparisons have been made between MTF measurements using these patterns and results obtained through direct measurements with the transmissive slanted-edge target and sine target.

Data compression studies for NOAA Hyperspectral Environmental Suite (HES) using 3D integer wavelet transforms with 3D set partitioning in hierarchical trees

Abstract: The next-generation NOAA/NESDIS GOES-R hyperspectral sounder, now referred to as the HES (Hyperspectral Environmental Suite), will have hyperspectral resolution (over one thousand channels with spectral widths on the order of 0.5 wavenumber) and high spatial resolution (less than 10 km). Hyperspectral sounder data is a particular class of data requiring high accuracy for useful retrieval of atmospheric temperature and moisture profiles, surface characteristics, cloud properties, and trace gas information. Hence compression of these data sets is better to be lossless or near lossless. Given the large volume of three-dimensional hyperspectral sounder data that will be generated by the HES instrument, the use of robust data compression techniques will be beneficial to data transfer and archive. In this paper, we study lossless data compression for the HES using 3D integer wavelet transforms via the lifting schemes. The wavelet coefficients are processed with the 3D set partitioning in hierarchical trees (SPIHT) scheme followed by context-based arithmetic coding. SPIHT provides better coding efficiency than Shapiro's original embedded zerotree wavelet (EZW) algorithm. We extend the 3D SPIHT scheme to take on any size of 3D satellite data, each of whose dimensions need not be divisible by 2 N , where N is the levels of the wavelet decomposition being performed. The compression ratios of various kinds of wavelet transforms are presented along with a comparison with the JPEG2000 codec.

Assessing spatial variability of soil water content through Thermal Inertia and NDVI

Abstract: AVHRR (Advanced Very High Resolution Radiometer on board NOAA satellites) data are considered here to evaluate the possibility of using the surface temperature as an indicator of the soil/canopy water content at the short time-scale. This is obtained by means of an indirect approach based on a simplified soil-atmosphere energy balance. The techniques provide sufficiently detailed coverage of the processes in terms of the time and spatial scale with respect to hydrological applications. Two different approaches have been tried: the first based on thermal inertia measurements (Xue & Cracknell, 1995)1 through ATI (Apparent Thermal Inertia), the second based on surface temperature (LST) and vegetation indices (NDVI), with the TVDI (Temperature Vegetation Dryness Index) suggested by Sandholt et al. (2002)2. Both techniques were used in detecting moist areas in a single image (or day/night images), and in multitemporal multitemporal applications. In particular, a new cloud detection algorithm, based on the bimodal frequency distribution of the infrared brightness temperatures (Ch 5 AVHRR) when clouds affect the image, has been proposed for ATI. As regards TVDI, a modified technique has been proposed for fixing the warm edge of the triangle based on the detection of the extreme dryness conditions on a monthly basis. The modified TVDI has been tested in comparison with an antecedent precipitation index (API) for moisture detection in single images. The substitution of day/night land surface temperature differences instead of noon temperatures in the "triangle method" has been also tested with good results in the multitemporal approach. Application of the proposed techniques can allow one to track the evolution of soil moisture in space and time and to improve the knowledge on the relationship between vegetation (NDVI) and soil moisture dynamics.

Airborne test results for smart pushbroom imaging system with optoelectronic image correction

Abstract: Smart pushbroom imaging system (SMARTSCAN) solves the problem of image correction for satellite pushbroom cameras which are disturbed by satellite attitude instability effects. Satellite cameras with linear sensors are particularly sensitive to attitude errors, which cause considerable image distortions. A novel solution of distortions correction is presented, which is based on the real-time recording of the image motion in the focal plane of the satellite camera. This allows using such smart pushbroom cameras (multi-/hyperspectral) even on moderately stabilised satellites, e.g. small sat's, LEO comsat's. The SMARTSCAN concept uses in-situ measurements of the image motion with additional CCD-sensors in the focal plane and real-time image processing of these measurements by an onboard Joint Transform Optical Correlator. SMARTSCAN has been successfully demonstrated with breadboard models for the Optical Correlator and a Smart Pushbroom Camera at laboratory level (satellite motion simulator on base of a 5 DOF industrial robot) and by an airborne flight demonstration in July 2002. The paper describes briefly the principle of operation of the system and gives a description of the hardware model are provided. Detailed results of the airborne tests and performance analysis are given as well as detailed tests description.

SCIAMACHY on ENVISAT: in-flight optical performance and first results

Abstract: The Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) is a contribution to the ENVISAT-1 satellite, which has been launched in March 2002. The SCIAMACHY instrument measures sunlight transmitted, reflected and scattered by the Earth's atmosphere or surface simultaneously from the UV to the SWIR spectral region (214 - 2380 nm) in nadir, limb, and occultation viewing geometry. SCIAMACHY allows the characterisation of the composition of the Earth atmosphere from the ground to the mesosphere. This paper gives an overview of the SCIAMACHY instrument and its in-flight detector, spectral and radiometric performance. Furthermore first results on trace gas retrieval from limb and nadir measurement mode will be summarised.

Status and developments in EOSTAR, a model to predict IR sensor performance in the marine environment

Abstract: The application of long-range infrared observation systems is challenging, especially with the currently available high spatial resolution infrared camera systems with resolutions comparable with their visual counterparts. As a result of these developments, the obtained infrared images are no longer limited by the quality of system but by atmospheric effects instead. For instance, atmospheric transmission losses and path radiance reduce the contrast of objects in the background and optical turbulence limits the spatial resolution in the images. Furthermore, severe image distortion can occur due to atmospheric refraction, which limits the detection and identification of objects at larger range. EOSTAR is a computer program under development to estimate these atmospheric effects using standard meteorological parameters and the properties of the sensor. Tools are provided to design targets and to calculate their infrared signature as a function of range, aspect angle, and weather condition. Possible applications of EOSTAR include mission planning, sensor evaluation and selection, and education. The user interface of EOSTAR is fully mouse-controlled, and the code runs on a standard Windows-based PC. Many features of EOSTAR execute almost instantaneous, which results in a user friendly code. Its modular setup allows its configuration to specific user needs and provides a flexible output structure.