Satellite Monitoring of the Biomass Production in Southern Greenland

Birger Ulf Hansen: Satellite Monitoring of the Biomass Production in Southern Greenland. Geografisk Tidsskrift 88:94–99. Copenhagen, 1988.

Based on satellite data from Southern Greenland the application of Normalized Difference Vegetation Index (NDVI) for monitoring biomass production has been evaluated. Field measurements of spectral reflectance data are quantitatively correlated with clipped samples of total above-ground biomass production. The relation between NDVI measured on the ground and biomass production is discussed. The seasonal and geographical variation in NDVI is correlated with the climate and water balance. The potential production is estimated as the product of mean NDVI and the length of the growing season. The results suggest that operational satellite monitoring of NDVI provides valuable assistance in agricultural management and forward planning of the potential breeding capacity in an arctic/subarctic environment.     

Coronal disturbances

A fast coronal transient event was observed simultaneously on 17 February 1972 by the Sacramento Peak Observatory 6-in. λ 5303 filter coronagraph and the High Altitude Observatory K-coronameter. We interpret the rapid opening of green line structure cospatial with the disappearance of a white light streamer as material motion of iron ions and electrons. Together with the subsequent two-fold increase in K-corona brightness in an adjacent region, this is taken as evidence of a transference of electrons to a new streamer in a realignment of magnetic flux tubes accompanying a flare.     

Progress in NTHMP Hazard Assessment

The Hazard Assessment component of the U.S. National Tsunami Hazard Mitigation Program has completed 22 modeling efforts covering 113 coastal communities with an estimated population of 1.2 million residents that are at risk. Twenty-three evacuation maps have also been completed. Important improvements in organizational structure have been made with the addition of two State geotechnical agency representatives to Steering Group membership, and progress has been made on other improvements suggested by program reviewers.     

The transition from pyroxene granulite facies to garnet clinopyroxene granulite facies. Experiments in the system CaO-MgO-Al2O3-SiO2

The pressure-temperature curve for the equilibrium anorthite+2enstatite=pyrope+diopside+quartz has been determined in the system CaO-MgO-Al₂O₂-SiO₂ to be between 13.4 and 14.0 kbars at 900° C. The slope up to 1,240° C is 8.5 bar/K. The entropy change at 1,200 K is 20 kJ. These data, combined with data from the literature, lead to a geobarometer equation which, when applied to rocks from the Agto area (West Greenland), gives pressure estimates of 6–10 kbars at 800° C. The results are consistent for rocks of differing Fe/Mg ratios and are consistent with independent pressure estimates.     

Seasonal Growth and Senescence of a Zostera marina Seagrass Meadow Alters Wave-Dominated Flow and Sediment Suspension Within a Coastal Bay

Tidally driven flows, waves, and suspended sediment concentrations were monitored seasonally within a Zostera marina seagrass (eelgrass) meadow located in a shallow (1–2 m depth) coastal bay. Eelgrass meadows were found to reduce velocities approximately 60 % in the summer and 40 % in the winter compared to an adjacent unvegetated site. Additionally, the seagrass meadow served to dampen wave heights for all seasons except during winter when seagrass meadow development was at a minimum. Although wave heights were attenuated across the meadow, orbital motions caused by waves were able to effectively penetrate through the canopy, inducing wave-enhanced bottom shear stress (τ _b ). Within the seagrass meadow, τ _b was greater than the critical stress threshold (=0.04 Pa) necessary to induce sediment suspension 80–85 % of the sampling period in the winter and spring, but only 55 % of the time in the summer. At the unvegetated site, τ _b was above the critical threshold greater than 90 % of the time across all seasons. During low seagrass coverage in the winter, near-bed turbulence levels were enhanced, likely caused by stem–wake interaction with the sparse canopy. Reduction in τ _b within the seagrass meadow during the summer correlated to a 60 % reduction in suspended sediment concentrations but in winter, suspended sediment was enhanced compared to the unvegetated site. With minimal seagrass coverage, τ _b and wave statistics were similar to unvegetated regions; however, during high seagrass coverage, sediment stabilization increased light availability for photosynthesis and created a positive feedback for seagrass growth.     

Low-cost long-term monitoring of global climate forcings and feedbacks

We describe the rationale for long-term monitoring of global climate forcings and radiative feedbacks as a contribution to interpretation of long-term global temperature change. Our discussion is based on a more detailed study and workshop report (Hansenet al., 1993b). We focus on the potential contribution of a proposed series of inexpensive small satellites, but we discuss also the need for complementary climate process studies and ground-based measurements. Some of these measurements could be made inexpensively by students, providing both valuable climate data and science educational experience.     

Vagn Walfrid Ekman

Ohne Zusammenfassung

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Vagn Walfrid Ekman

     

Die Ermittlung der Gezeiten beliebig gestalteter Meeresgebiete mit Hilfe des Randwertverfahrens

Zusammenfassung Es wird ein Randwertverfahren entwickelt, das gestattet, die Gezeiten eines beliebig gestalteten Meeresgebietes in eindeutiger Weise allein aus den Beobachtungen am Rande zu ermitteln. Die Brauchbarkeit des Verfahrens wird am Beispiel des Englischen Kanals gezeigt.

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The computation of the tides in ocean areas of any shape by means of the method of boundary values

Summary In the following paper a method of boundary values is developed by which the tides of ocean areas of any shape can be computed. The validity of the method is demonstrated for the English Channel by comparing the computed values of the principal semidiuranal lunar tide with the observed values.