XVIIIth International Congress of Photogrammetry and Remote Sensing

The XVIIIth International Congress of Photogrammetry and Remote Sensing was held in the Austria Center, Vienna from 9th to 19th July, 1996. Reports on the Technical Commission Activities, on the Congress Exhibition and on the General Assembly were given at a meeting of the Photogrammetric Society on 7th October, 1996. Papers from the Congress were published in the International Archives of Photogrammetry and Remote Sensing, 31.     

Shapes of annual frequency distributions of wind speed observed on high meteorological masts

Annual wind distributions from six masts are used to investigate the annual variability of hourly-average wind. A variability extremum occurs at the height where the average diurnal cycle of wind reverses its phase from a nocturnal minimum to a nocturnal maximum. A simple profile model shows that in non-complex terrain, this reversal height varies approximately between 50 m at coasts and 90 m inland. The Weibull distribution shape factor k has a maximum at the reversal height, and with decreasing height, k decreases approximately as a linear function of height. Therefore estimation of wind distribution shape from surface data is possible in the surface layer. In the upper PBL, however, such estimation is not very feasible, because no simple methods are available to estimate the reversal height from routine surface observations.Also: Dept. of Applied Physics, Technical University, Delft, Netherlands.     

The petrogenesis of 30–20 Ma basic and intermediate volcanics from the Mogollon-Datil Volcanic Field,New Mexico,USA

In the western USA calcalkaline magmas were generated hundreds of kilometres from the nearest destructive plate margin, and in some areas during regional extension several Ma after the cessation of subduction. The Mogollon-Datil Volcanic Field (MDVF) in southern New Mexico was a centre of active magmatism in the mid- to late-Tertiary, and a detailed field, petrographic and geochemical study has been undertaken to evaluate the relations between extensional tectonics and calcalkaline magmatism in the period 30–20 Ma. The rocks comprise alkalic to high-K calcalkaline lavas, ranging from basalt to high silica andesitc. Most of the basaltic rocks have relatively low HFSE abundances, elevated ⁸⁷Sr/⁸⁶Sr and low ¹⁴³Nd/¹⁴⁴Nd, similar to many Tertiary basalts across the western USA, and they are inferred to have been derived from the continental mantle lithosphere. Two differentiation trends are recognised, with the older magmas having evolved to more calcalkaline compositions by magma mixing between alkalic basaltic andesites and silicic crustal melts, and the younger rocks having undergone 30–40% fractional crystallisation to more alkalic derivatives. The younger basalts also exhibit a shift to relatively higher HSFE abundances, with lower ⁸⁷Sr/⁸⁶Sr and higher ¹⁴³Nd/¹⁴⁴Nd, and these have been modelled as mixtures between an average post-5 Ma Basin and Range basalt and the older MDVF lithosphere-derived basalts. It is argued that the presence of subduction-related geochemical signatures and the development of calcalkaline andesites in the 30–20 Ma lavas from the MDVF are not related to the magmatic effects of Tertiary subduction. Rather, basic magmas were generated by partial melting of the lithospheric mantle which had been modified during a previous subduction event. Since these basalts were generated at the time of maximum extension in the upper crust it is inferred that magma generation was in response to lithospheric extension. The association of the 30–20 Ma calcalkaline andesites with the apparently anorogenic tectonism of late mid-Tertiary extension, is the result of crustal contamination, in that fractionated, mildly alkaline, basaltic andesite magmas were mixed with silicic crustal melts, generating hybrid andesite lavas with calcalkaline affinities.     

Differential responses of zooplankton populations (Bosmina longirostris) to fish predation and nutrient-loading in an introduced and a natural sockeye salmon nursery lake on Kodiak Island, Alaska, USA

Stratigraphic changes in the remains of Bosmina longirostris from a lake with an introduced sockeye salmon population and a lake with a natural salmon run on Kodiak Island demonstrated markedly different responses to past fluctuations in salmon populations. In both lakes, there was a positive correlation between the density of Bosmina microfossils and the abundance of sockeye salmon. However, opposite size trends were observed in the two lakes. In Karluk Lake, which has a native sockeye salmon population, Bosmina mean carapace lengths were largest at high salmon densities, and mean mucro and antennule lengths were also large, suggesting strong predation pressure from cyclopoid copepods, and less intense pressure from juvenile sockeye salmon. As salmon-derived nutrients are important in driving primary productivity in this system, changes in zooplankton productivity track salmon escapement, but grazing pressure on Bosmina from juvenile salmon is less important than that from cyclopoid copepods. In Frazer Lake, a lake with an introduced salmon population, Bosmina morphologies were smallest during periods of high sockeye salmon in the lake, suggesting much stronger predation effects from sockeye salmon due to the suppression of Cyclops columbianus. Latent development of compensatory mechanisms and the delayed recovery of copepod populations to salmon introductions has resulted in zooplankton populations that are still recovering from shifts in fish populations that occurred decades earlier. The differential response of Bosmina populations between the natural and manipulated lakes suggests that care must be taken when attempting to extrapolate results from whole-lake manipulations and short-term experiments to natural systems.