Evaluation of the geometric stability and the accuracy potential of digital cameras — Comparing mechanical stabilisation versus parameterisation

Recent tests on the geometric stability of several digital cameras that were not designed for photogrammetric applications have shown that the accomplished accuracies in object space are either limited or that the accuracy potential is not exploited to the fullest extent. A total of 72 calibrations were calculated with four different software products for eleven digital camera models with different hardware setups, some with mechanical fixation of one or more parts. The calibration procedure was chosen in accord to a German guideline for evaluation of optical 3D measuring systems [VDI/VDE, VDI/VDE 2634 Part 1, 2002. Optical 3D Measuring Systems–Imaging Systems with Point-by-point Probing. Beuth Verlag, Berlin]. All images were taken with ringflashes which was considered a standard method for close-range photogrammetry. In cases where the flash was mounted to the lens, the force exerted on the lens tube and the camera mount greatly reduced the accomplished accuracy. Mounting the ringflash to the camera instead resulted in a large improvement of accuracy in object space. For standard calibration best accuracies in object space were accomplished with a Canon EOS 5D and a 35 mm Canon lens where the focusing tube was fixed with epoxy (47  μm maximum absolute length measurement error in object space). The fixation of the Canon lens was fairly easy and inexpensive resulting in a sevenfold increase in accuracy compared with the same lens type without modification. A similar accuracy was accomplished with a Nikon D3 when mounting the ringflash to the camera instead of the lens (52  μm maximum absolute length measurement error in object space). Parameterisation of geometric instabilities by introduction of an image variant interior orientation in the calibration process improved results for most cameras. In this case, a modified Alpa 12 WA yielded the best results (29  μm maximum absolute length measurement error in object space). Extending the parameter model with FiBun software to model not only an image variant interior orientation, but also deformations in the sensor domain of the cameras, showed significant improvements only for a small group of cameras. The Nikon D3 camera yielded the best overall accuracy (25  μm maximum absolute length measurement error in object space) with this calibration procedure indicating at the same time the presence of image invariant error in the sensor domain. Overall, calibration results showed that digital cameras can be applied for an accurate photogrammetric survey and that only a little effort was sufficient to greatly improve the accuracy potential of digital cameras.     

A concept for global access to information on geographical databases

Monitoring of the ecological as well as economical aspects of the planet Earth will in future require more sophisticated data obtaining systems (e. g. satellites) and data processing devices (e. g. GIS). In order to process the great amount of data, detailed information on geographical databases has to be provided in an easy way. In this paper a concept of an information system on geographical databases is presented which encompasses a centrally managed international directory with summary information as well as local information interfaces geographical databases. An information interface provides detailed information on the extent, structure and geographical meaning of the data stored in the geographical database belonging to it. To describe this information a conceptual scheme, based on an object oriented approach, is developed.     

Variation in upwelling intensity along the NorthWest Iberian Peninsula (Galicia)

Thermohaline variables were simultaneously measured, July 17, 2000, at four Galician rias under favourable upwelling conditions to analyse upwelling intensity. The intensity of coastal upwelling is shown to be strongly dependent on the wind pattern. The maximum amplitudes of wind stress were observed at the western coast (0.30 Nm^-2) with southward direction (favourable to upwelling) and these are shown to be related to low temperature (12°C) and high salinity (35.8) in the estuaries mouth. From Cape Finisterre to Cape Estaca de Bares the wind stress showed a lower magnitude (0.05-0.10 Nm^-2) with a direction oblique to the coast. The temperature showed an increase (14°C) and the salinity a decrease (35.4) because the lower upwelling intensity at this part of the coast. The observed decrease in upwelling from south to north is not an isolated event, since the measured wind conditions are persistent during summer months, at least in the period with available QuikSCAT data (1999-2004).     

Quality control algorithms for rainfall measurements

One of the basic requirements for a scientific use of rain data from raingauges, ground and space radars is data quality control. Rain data could be used more intensively in many fields of activity (meteorology, hydrology, etc.), if the achievable data quality could be improved. This depends on the available data quality delivered by the measuring devices and the data quality enhancement procedures. To get an overview of the existing algorithms a literature review and literature pool have been produced. The diverse algorithms have been evaluated to meet VOLTAIRE objectives and sorted in different groups. To test the chosen algorithms an algorithm pool has been established, where the software is collected. A large part of this work presented here is implemented in the scope of the EU-project VOLTAIRE (Validation of multisensors precipitation fields and numerical modeling in Mediterranean test sites).     

Thermal surface characteristics of coal fires 1 results of in-situ measurements

Natural underground coal fires are fires in coal seams occurring subsurface. The fires are ignited through a process named spontaneous combustion, which occurs based on a natural reaction but is usually triggered through human interaction. Coal mining activities expose coal to the air. This leads to the exothermal oxidation of the carbon in the coal with the air's oxygen to CO₂ and – under certain circumstances – to spontaneous combustion. Coal fires occur in many countries world wide – however, currently the Chinese coal mining industry faces the biggest problems with coal fires. Coal fires destroy the valuable resource coal and furthermore lead to many environmental degradation phenomena such as the deterioration of surrounding vegetation, land subsidence and the emission of toxic gasses (CO, N₂O). They additionally contribute to the emission of green house relevant gasses such as CO₂ and CH₄ to the atmosphere.In this paper we present thermal characteristics of coal fires as measured in-situ during a field campaign to the Wuda coal fire area in south-central Inner Mongolia, China. Thermal characteristics include temperature anomaly measurements at the surface, spatial surface temperature profiles of fire areas and unaffected background areas, diurnal temperature profiles, and temperature measurements inside of coal fire induced cracks in the overlying bedrock. For all the measurements the effects of uneven solar heating through influences of slope and aspect are considered.Our findings show that coal fires result in strong or subtle thermal surface anomalies. Especially the latter can easily be influenced by heating of the surrounding background material through solar influences. Temperature variation of background rocks with different albedo, slope, aspect or vegetation cover can substantially influence the detectability of thermal anomalies. In the worst case coal fire related thermal anomalies can be completely masked by solar patterns during the daytime. Thus, night-time analysis is the most suitable for thermal anomaly mapping of underground coal fires, although this is not always feasible. The heat of underground coal fires only progresses very slowly through conduction in the rock material. Anomalies of coal fires completely covered by solid unfractured bedrock are very weak and were only measured during the night. The thermal pattern of underground coal fires manifested on the surface during the daytime is thus the pattern of cracks and vents, which occur due to the volume loss underground and which support radiation and convective energy transport of hot gasses. Inside coal fire temperatures can hardly be measured and can only be recorded if the glowing coal is exposed through a wider crack in the overlaying bedrock. Direct coal fire temperatures measured ranged between 233 °C and 854 °C. The results presented can substantially support the planning of thermal mapping campaigns, analyses of coal fire thermal anomalies in remotely sensed data, and can provide initial and boundary conditions for coal fire related numerical modeling.In a second paper named “Thermal Characteristics of Coal Fires 2: results of measurements on simulated coal fires” [Zhang J., Kuenzer C., Tetzlaff A., Oettl D., Zhukov B., Wagner W., 2007. Thermal Characteristics of Coal Fires 2: Result of measurements on simulated coal fires. Accepted for publication at Journal of Applied Geophysics. doi:10.1016/j.jappgeo.2007.08.003] we report about thermal characteristics of simulated coal fires simulated under simplified conditions. The simulated set up allowed us to measure even more parameters under undisturbed conditions — especially inside fire temperatures. Furthermore we could demonstrate the differences between open surface coal fires and covered underground coal fires. Thermal signals of coal fires in near range thermal remotely sensed imagery from an observing tower and from an airplane are presented and discussed.     

Crust and Upper Mantle Structure in the Caribbean Region by Group Velocity Tomography and Regionalization

An overview of the crust and upper mantle structure of Central America and the Caribbean region is presented as a result of the processing of more than 200 seismograms recorded by digital broadband stations from SSSN and GSN seismic networks. Group velocity dispersion curves are obtained in the period range from 10s to 40s by FTAN analysis of the fundamental mode of the Rayleigh waves; the error of these measurements varies from 0.06 and 0.09 km/s. From the dispersion curve, seven tomographic maps at different periods and with average spatial resolution of 500 km are obtained. Using the logical combinatorial classification techniques, eight main groups of dispersion curves are determined from the tomographic maps and eleven main regions, each one characterized by one kind of dispersion curves, are identified. The average dispersion curves obtained for each region are extended to 150s by adding data from a larger-scale tomographic study (Vdovin et al., 1999) and inverted using a nonlinear procedure. A set of models of the S-wave velocity vs. depth in the crust and upper mantle is found as a result of the inversion process. In six regions we identify a typically oceanic crust and upper mantle structure, while in the other two the models are consistent with the presence of a continental structure. Two regions, located over the major geological zones of the accretionary crust of the Caribbean region, are characterized by a peculiar crust and upper mantle structure, indicating the presence of lithospheric roots reaching, at least, about 200 km of depth.     

The 1631 Vesuvius eruption. A reconstruction based on historical and stratigraphical data

The eruption of 1631 A.D. was the most violent and destructive event in the recent history of Vesuvius. More than fifty primary documents, written in either Italian or Latin, were critically examined, with preference given to the authors who eyewitnessed volcanic phenomena. The eruption started at 7 a.m. on December 16 with the formation of an eruptive column and was followed by block and lapilli fallout east and northeast of the volcano until 6 p.m. of the same day. At 10 a.m. on December 17, several nuées ardentes were observed to issue from the central crater, rapidly descending the flanks of the cone and devastating the villages at the foot of Vesuvius. In the night between the 16th and 17th and on the afternoon of the 17th, extensive lahars and floods, resulting from rainstorms, struck the radial valleys of the volcano as well as the plain north and northeast.Deposits of the eruption were identified in about 70 localities on top of an ubiquitous paleosol formed during a long preeruptive volcanic quiescence. The main tephra unit consists of a plinian fallout composed of moderately vesicular dark green lapilli, crystals and lithics. Isopachs of the fallout are elongated eastwards and permit a conservative volume calculation of 0.07 km³. The peak mass flux deduced from clast dispersal models is estimated in the range 3–6 × 10⁷ kg/s, corresponding to a column height of 17–21 km. East of the volcano the plinian fallout is overlain by ash-rich low-grade ignimbrite, surges, phreatomagmatic ashes and mud flows. Ash flows occur in paleovalleys around the cone of Vesuvius but are lacking on the Somma side, suggesting that pyroclastic flows had not enough energy to overpass the caldera wall of Mt. Somma. Deposits are generally unconsolidated, massive with virtually no ground layer and occasionally bearing sparse rests of charred vegetation. Past interpretations of the products emitted on the morning of December 17 as lava flows are inconsistent with both field observations and historical data. Features of the final phreatomagmatic ashes are suggestive of alternating episodes of wet ash fallout and rainfalls. Lahars interfingered with primary ash fallout confirm episodes of massive remobilization of loose tephra by heavy rainfalls during the final stage of the eruption.Chemical analyses of scoria clasts suggest tapping of magma from a compositionally zoned reservoir. Leucite-bearing, tephritic-phonolite (SiO₂ 51.17%) erupted in the early plinian phase was in fact followed by darker and slightly more mafic magma richer in crystals (SiO₂ 49.36%). During the nuées ardentes phase the composition returned to that of the early phase of the eruption.The reconstruction of the 1631 eruptive scenario supplies new perspectives on the hazards related to plinian eruptions of Vesuvius.     

Solar wind density model from km-wave type III bursts

Solar radio bursts were observed with a 4-channel radiometer and polarization analyser at wavelenghts around 12 m. The time and frequency resolutions were 10 ms and 100 kHz respectively. Observations on the duration, time profile and frequency splitting are described.