Spectroradiometric requirements for the reflective module of the airborne spectrometer ARES

The Airborne Reflective/Emissive Spectrometer is specified as a whisk-broom imaging spectrometer for remote sensing of land surfaces covering the wavelength regions 0.47-2.45 /spl mu/m and 8-12 /spl mu/m with 160 spectral bands. The instrument is being built by Integrated Spectronics, financed by the German Aerospace Agency (DLR) and the GeoResearch Centre Potsdam (GFZ) and will be available to the scientific community from end 2005 on. The spectroradiometric design is based on scientific requirements derived from three main application scenarios comprising vegetation, soil, and mineral sciences. Two of these are described in this letter. Measured or modeled reflectance spectra are input to a simulation model that calculates at-sensor radiance spectra, resamples them with the channel-specific response functions, adds different amounts of noise in the radiance domain, and performs a retrieval to get the corresponding noisy surface reflectance spectra. The retrieval results as a function of the sensor noise level are compared with the accuracy requirements imposed by the different application fields taking into account the technical boundary conditions. The final specifications account for the most demanding requirements of the three application fields: a spectral sampling distance of 13-14 nm in the 470-1800 nm region, and 12 nm in the 2000-2450-nm region. The required noise-equivalent radiances are 5, 3, and 2 nW/spl middot/cm/sup -2//spl middot/sr/sup -1//spl middot/nm/sup -1/ for the spectral regions 470-1000, 1000-1800, and 2000-2450 nm, respectively.     

The response of circulation and salinity in a micro-tidal estuary to sub-tidal oscillations in coastal sea surface elevation

Conceptual models of circulation theorise that the dominant forces controlling estuarine circulation are freshwater discharge from the riverine section (landward), tidal forcing from the ocean boundary, and gravitational circulation resulting from along-estuary gradients in density. In micro-tidal estuaries, sub-tidal water level changes (classified as those with periods between 3 and 10 days) with amplitudes comparable to the spring tidal range can significantly influence the circulation and distribution of water properties. Field measurements obtained from the Swan River Estuary, a diurnal, micro-tidal estuary in south-western Australia, indicated that sub-tidal water level changes at the ocean boundary were predominantly from remotely forced continental shelf waves (CSWs). The sub-tidal water levels had maximum amplitudes of 0.8 m, were comparable to the maximum tidal range of 0.6 m, propagated into the estuary to its tidal limit, and modified water levels in the whole estuary over several days. These oscillations dominated the circulation and distribution of water properties in the estuary through changing the salt wedge location and increasing the bottom water salinity by 7 units over 3 days. The observed salt wedge excursion forced by CSW was up to 5 km, whereas the maximum tidal excursion was 1.2 km. The response of the residual currents and the salinity distribution lagged behind the water level changes by ∼24 h. It was proposed that the sub-tidal forcing at the ocean boundary, which changed the circulation, salinity, and dissolved oxygen in the upper estuary, was due to a combination of two processes: (1) a gravity current generated by a process similar to a lock exchange mechanism and (2) amplified along-estuary density gradients in the upper estuary, which enhanced the gravitational circulation in the estuary. The salt intrusions under the sub-tidal forcing caused the rapid movement of anoxic water upstream, with significant implications for water quality and estuarine health.     

A magnetic survey of Explorer Seamount— Recent spreading at the Explorer trench

In 1981 a magnetic and bathymetric survey was carried out over Explorer Seamount located approximately between 48°50′ and 49°30′N and 130°40′ and 131°30′W. During the cruise four pillow fragments were dredged from peaks in this area. Based on the observed magnetic data, it was identified that the main peak of Explorer Seamount should be of the Bruhnes age while the magnetic high in the NW of study area would be Gauss. This would yield a spreading rate of about 2 cm per year for the Matuyama epoch. The results of intensities of remanence measured from the pillow fragments indicate that the ages are less than 10⁶ years. Similarly the Curie temperature is consistent with ages of around 10⁶ years. An attempt was made to model the observed magnetic field using a series of uniformly magnetized NE-SW trending blocks of alternating polarity. Agreement between the model and observed results is satisfied. Oxidation ratios calculated from measured samples suggest that the main peak of Explorer Seamount is not far from the present day ridge axis, which agrees with the younger interpretation from the magnetic profiles. The results mentioned above strongly, but not conclusively, favour an interpretation in which the southeastern peak of Explorer Seamount is of the Bruhnes age and the recent spreading is at Explorer trench, then the Sovanco Fracture Zone should be thought of as a complex triangular area between the northern end of Juan de Fuca Ridge and Explorer Seamount rather than as a simple transform fault as defined conventionally.     

The variation of the mean size of the photospheric granules close to and away from a sunspot

We study the mean size of granules as a function of distance from the boundaries of the sunspot penumbra. We use for the determination of the mean size two different methods, a visual and a photometric. In all cases the mean diameter of the granules away from the spot was greater than the mean diameter of the granules in the neighbourhood of the penumbra. Our study is based on an excellent sequence of photos, taken at the Pic-du-Midi Observatory on May 11, 1979.     

Periglacial microjointing and faulting in Weichselian fluvio-aeolian deposits

A Weichselian Late Pleniglacial fluvio-aeolian deposit has been investigated in the southern Netherlands. Three main structural lineaments have been distinguished: (1) very small, vertical platy structures (microjoints), in a parallel and a columnar configuration; (2) large joints and normal faults with minor displacement (‘Grubbenvorst type’), arranged in a conjugate fault-system; (3) large joints and normal faults (‘wedge-type’), located adjacent to ice-wedge casts. Since clay is absent, the occurrence of the vertical platy structures cannot be attributed to desiccation cracking. The vertical platy structures are interpreted as the result of thermal contraction cracking of a relatively thin layer, due to a sudden temperature drop. The large joints and normal faults of the Grubbenvorst type are the result of failure of the sediment due to the melting of the permafrost in the Late Pleniglacial, just before the formation of the Beuningen Gravel Bed. In other areas large periglacial convolutions have been formed during the same period. The normal faults and joints of the wedge type are more generally known. They are the result of failure of the sediment adjacent to a melting ice wedge.     

QUALITY ASSESSMENT OF DIGITAL ELEVATION MODELS PRODUCED BY AUTOMATIC STEREOMATCHERS FROM SPOT IMAGE PAIRS

A number of published steromatching algorithms have been implemented and tested on SPOT images of areas for which gridded digital elevation models (DEMs) are available with spacings of 80 m or less, as well as ground control checkpoints. Results are presented for comparison of stereomatched output with the DEMs as well as an analysis of the errors arising and their causes. Results are discussed for planimetrically geocoded and epipolar resampled data. An error budget describing effects due to orientation, feature localisation and matching are discussed and conclusions drawn for future work in this area.     

Reliability of Chemical Analyses of Water Samples — The Experience of the UMTRA Project

Ground water quality investigations require reliable chemical analyses of water samples. Unfortunately, laboratory analytical results are often unreliable. The Uranium Mill Tailings Remedial Action (UMTRA) Project's solution to this problem was to establish a two-phase quality assurance program for the analysis of water samples. In the first phase, eight laboratories analyzed three solutions of known composition. The analytical accuracy of each laboratory was ranked and three laboratories were awarded contracts. The second phase consists of on-going monitoring of the reliability of the selected laboratories.
The following conclusions are based on two years of experience with the UMTRA Project's Quality Assurance Program:
• The reliability of laboratory analyses should not be taken for granted.
• Analytical reliability may be independent of the prices charged by laboratories.
• Quality assurance programs benefit both the customer and the laboratory.