Fire Danger Monitoring Using ERS-1 SAR Images in the Case of Northern Boreal Forests

Research was carried out to assess the potential of imaging radar systems formonitoring forest fire danger. In Canada, daily forest fire danger ratings are generated by the Canadian ForestFire Danger Rating System (CFFDRS), based on estimates of fire weather indices (FWI) and measured foliar moisturecontent (FMC). To evaluate the potential of imaging radar, an experiment was conducted using test sitesconsisting of jack pine, black spruce and white spruce stands located in the MacKenzie river basin, NorthwestTerritories, Canada. Radar image intensity values from ERS-1 SAR imagery collected over these stands in 1994 werecompared to FWI indices and FMC data. FWI indices were calculated using data from local weather stations.Seasonal trends in radar backscatter (⁰) were shown to correlate with temperature and precipitation. Significant relationships were found between ⁰ and FWI codes and indices, particularly in thecase of the black spruce stands, with slow-drying fuels, like duff moisture code (DMC), drought code (DC), and build-upindex (BUI). Rates of changes in ⁰were related to rates of changes in FMC, particularly in the case ofthe jack pine stands for old FMC and in the case of white spruce stands for composite FMC.     

Recent sedimentary development of Tampa Bay, Florida: A microtidal estuary incised into tertiary platform carbonates

Tampa Bay, a large, microtidal, clastic-filled estuary incised into Tertiary carbonate strata, is the largest estuary on Florida’s west coast. A total of 250 surface sediment samples and 17 cores were collected in Tampa Bay in order to determine the patterns and controlling factors governing the recent infilling and modern sediment distribution, and to examine the results in terms of current models of estuarine sedimentation and development. Surficial sediments in Tampa Bay consist of three facies types, each occurring in a distinct zone: modern terrigenous clastic muds occurring in the upper bay and around the bay periphery; relict, reworked-fluvial, quartz-rich sands occupying the open portion of the middle bay; and modern carbonate-rich, marine-derived sands and gravels occupying the lower bay. Factors controlling sediment distribution include: sediment source and supply rate; bathymetry, which is a function of the antecedent topography; and the winnowing effect of wind-generated waves that prohibits modern accumulation in the shallow middle bay. These factors also play a major role in the recent infilling history of Tampa Bay, which has progressed in four stages during the Holocene sea-level rise. Recently developed models of estuarine sedimentation are based primarily on mesotidal to macrotidal estuaries in terrigenous clastic settings in which sedimentation patterns and infilling history are a result of the relative contribution of marine and fluvial processes. Tampa Bay differs in that it was originally incised into carbonate strata, and neither fluvial or marine processes are interpreted to be major contributors to modern sediment distribution. Tampa Bay, therefore, provides an example of an unusual estuary type, which should be considered in future modeling efforts. *** DIRECT SUPPORT *** A01BY083 00004     

Observations and modelling of spectral energy distributions of carbon stars with optically thin envelopes

We present broad-band photometry in the optical, near-infrared and submillimetre, and mid-infrared spectrophotometry of a selection of carbon stars with optically thin envelopes. Most of the observations were carried out simultaneously.   Beside the emission feature at 11.3 μ m due to silicon carbide grains in the circumstellar environment, many of our mid-infrared spectra show an emission feature at 8.6 μ m. All the observed spectral energy distributions exhibit a very large far-infrared flux excess. Both these features are indeed common to many carbon stars surrounded by optically thin envelopes.   We have modelled the observed spectral energy distributions by means of a full radiative transfer treatment, paying particular attention to the features quoted above. The peak at 8.6 μ m is usually ascribed to the presence of hydrogenated amorphous carbon grains. We find also that the feature at 8.6 μ m might be reproduced by assuming that the stars have a circumstellar environment formed of both carbon- and oxygen-rich dust grains, although this is in contrast with what one should expect in a carbon-rich environment. The far-infrared flux excess is usually explained by the presence of a cool detached dust shell. Following this hypothesis, our models suggest a time-scale for the modulation of the mass-loss rate of the order of some 10³ yr.     

Stratigraphy of the upper Jurassic-lower cretaceous Nordenskjöld Formation of eastern Graham Land, Antarctica

The Nordenskjöld Formation is a sequence of thinly interbedded ash beds and black, radiolarian-rich mudstones which is exposed on the eastern coast of the Antarctic Peninsula. As a result of recent field work, the Nordenskjöld Formation has been re-examined and redefined with three new members recognized — the Longing, Ameghino, and Larsen members. The age of the formation, based on its macrofossil content, is Kimmeridgian to Berriasian, although reworked clasts from James Ross Island suggest it might range down into the Oxfordian.     

Line ratios for solar ultra-violet lines of Ov

New O v rate coefficients are used to calculate the ratio of the intensity of the 760 Å multiplet to that of the 630 Å line. Results are given for a range of electron densities and temperatures. The theoretical ratios are compared with observed line ratios for different solar regions.     

Do Archean chemical sediments record ancient seawater rare earth element patterns?

Rare earth elements (REE) concentrations of Archean and Proterozoic chemical sediments are commonly used as proxies to study secular trends in the geochemistry of Precambrian seawater. In addition, similarities in the REE signatures of Archean chemical sediments and modern seawater have led researchers to argue that some Archean rocks originated as biochemical precipitates (i.e., microbial carbonates) in shallow marine (e.g., peritidal) environments. However, terrestrial waters, including river water and groundwater, also commonly exhibit REE fractionation patterns that resemble modern seawater. Here, we present the seawater-like REE data for groundwaters from central México as additional evidence that these patterns are not unique to the marine environment. The shale-normalized REE patterns of the groundwaters are compared to those of modern seawater (open ocean and nearshore), Holocene reefal microbial carbonates and corals, and Archean chemical sediments using statistical means (i.e., ANOVA and Wilcoxon analyses) in order to quantify the similarities and/or differences in the REE patterns. Shale-normalized (SN) Ce anomalies and measures of REE fractionation [i.e., (La/Yb)_SN, (Pr/Yb)_SN, (Nd/Yb)_SN, and (Gd/Yb)_SN] of the central México groundwater samples are statistically indistinguishable from those of modern seawater. Moreover, except for differences in the Ce anomalies, which are lacking in Archean chemical sediments, the REE patterns of the central México groundwaters are also statistically similar to REE patterns of Archean chemical sediments, especially those of the 3.45 Ga Strelley Pool Chert. Consequently, we suggest that without additional information, it may be premature to unequivocally conclude that Archean chemical sediments record REE signatures of an Archean ocean.     

Electron density variations during ultraviolet transient events

% High-resolution temporal observations performed with the SUMER spectrometer on SOHO provide an opportunity to investigate the electron density variations in the `quiet-Sun' solar transition region due to UV transient events. Two datasets obtained in the density sensitive lines belonging to the Oiv 1400 Å multiplet were searched for such events, leading to the identification of two explosive events, on 10 July 1996 and 31 May 1997. In both cases, the Oiv 1401.16/1404.81 density-sensitive line intensity ratio shows a clear variation, corresponding to enhancements in the electron density by factors of 3. This is fully consistent with recent 2.5D MHD simulations. The 10 July 1996 dataset also provided us with the opportunity to monitor the behavior of the electron density through an UV blinker. Despite an increase of a factor of two in the line intensities, no variation of the electron density was found. This suggests that the intensity enhancement is due to an increase in the filling factor.     

Detection of Planetary Transits of the Star HD 209458 in the Hipparcos Data Set

A search of the Hipparcos satellite photometry data for the star HD 209458 reveals evidence for a planetary transit signature consistent with the planetary properties reported by Henry et al. and Charbonneau et al. and allows further refinement of the planet's orbital period. The long time baseline (about 2926 days or 830 periods) from the best Hipparcos transit-like event to the latest transit reported by Henry et al. for the night of 1999 November 15 (UT) allows for an orbital period determination of 3.524736 days with an uncertainty of 0.000045 days (3.9 s). The transit events observed by Charbonneau et al. fall at the interim times expected to within the errors of this newly derived period. A series of statistical tests was performed to assess the likelihood of these events occurring by chance. This was crucial given the ill-conditioned problem presented by the sparse sampling of the light curve and the non-Gaussian distribution of the points. Monte Carlo simulations using bootstrap methods with the actual Hipparcos HD 209458 data set indicate that the transit-like signals of the depth observed would only be produced by chance in 21 out of 1 million trials. The transit durations and depths obtained from the Hipparcos data are also consistent with those determined by Charbonneau et al. and Henry et al. within the limitations of the sampling intervals and photometric precision of the Hipparcos data.     

Facies architecture of a silicic intrusion-dominated volcanic centre at Highway–Reward, Queensland, Australia

The Highway–Reward massive sulphide deposit is hosted by a silicic volcanic succession in the Cambro-Ordovician Seventy Mile Range Group, northeastern Australia. Three principal lithofacies associations have been identified in the host succession: the volcanogenic sedimentary facies association, the primary volcanic facies association and the resedimented syn-eruptive facies association. The volcanogenic sedimentary facies association comprises volcanic and non-volcanic siltstone and sandstone turbidites that indicate submarine settings below storm wave base. Lithofacies of the primary volcanic facies association include coherent rhyolite, rhyodacite and dacite, and associated non-stratified breccia facies (autoclastic breccia and peperite). The resedimented volcaniclastic facies association contains clasts that were initially formed and deposited by volcanic processes, but then redeposited by mass-flow processes. Resedimentation was more or less syn-eruptive so that the deposits are essentially monomictic and clast shapes are unmodified. This facies association includes monomictic rhyolitic to dacitic breccia (resedimented autoclastic facies), siltstone-matrix rhyolitic to dacitic breccia (resedimented intrusive hyaloclastite or resedimented peperite) and graded lithic-crystal-pumice breccia and sandstone (pumiceous and crystal-rich turbidites). The graded lithic-crystal-pumice breccia and sandstone facies is the submarine record of a volcanic centre(s) that is not preserved or is located outside the study area. Pumice, shards, and crystals are pyroclasts that reflect the importance of explosive magmatic and/or phreatomagmatic eruptions and suggest that the source vents were in shallow water or subaerial settings.The lithofacies associations at Highway–Reward collectively define a submarine, shallow-intrusion-dominated volcanic centre. Contact relationships and phenocryst populations indicate the presence of more than 13 distinct porphyritic units with a collective volume of 0.5 km³. Single porphyritic units vary from <10 to 350 m in thickness and some are less than 200 m in diameter. Ten of the porphyritic units studied in the immediate host sequence to the Highway–Reward deposit are entirely intrusive. Two of the units lack features diagnostic of their emplacement mechanism and could be either lavas and intrusions. Direct evidence for eruption at the seafloor is limited to a single partly extrusive cryptodome. However, distinctive units of resedimented autoclastic breccia indicate the presence nearby of additional lavas and domes.The size and shape of the lavas and intrusions reflect a restricted supply of magma during eruption/intrusion, the style of emplacement, and the subaqueous emplacement environment. Due to rapid quenching and mixing with unconsolidated clastic facies, the sills and cryptodomes did not spread far from their conduits. The shape and distribution of the lavas and intrusions were further influenced by the positions of previously or concurrently emplaced units. Magma preferentially invaded the sediment, avoiding the older units or conforming to their margins. Large intrusions and their dewatered envelope may have formed a barrier to the lateral progression and ascent of subsequent batches of magma.     

Photometric modelling of starspots – II. The fortran code spotpic

A fortran code which computes synthetic light and colour curves of active, spotted stars has been developed. The main feature of this code is that it can simultaneously model the V light curve and the ( V − R )_c, ( V − I )_c, ( V − K ) colour data. It also uses new effective temperature–colour and Barnes–Evans-like calibrations, temperature and gravity-dependent limb darkening coefficients and different effective surface gravities for the spotted and unspotted photosphere. The code allows for two-component spots, i.e. spots with umbral and penumbral components. Various problematic spot configurations were investigated and we conclude that, in order to be able to differentiate spots with various thermal structures (umbrae, penumbrae, faculae) or polar spots from equatorial bands, the modelling of the infrared colours, especially ( V − I )_c and ( V − K ), is needed.