Monitoring Flood Extent and Forecasting Excess Runoff Risk with RADARSAT-1 Data

Earth observation from active microwave satellites such as RADARSAT-1 is an excellent tool to monitor and forecast floods. Two complementary approaches are described in this paper: (a) real time or near-real time monitoring of flood extent and (b) mapping of hydrological properties of drainage basins. Since it can penetrate through clouds, which usually occur during precipitation periods, and due to the fact that it can be programmed with different incidence angles, RADARSAT-1 enables frequent coverage over specific areas of interest. It has been used successfully to monitor a major flood of the Red River in Manitoba in 1997, by providing frequent coverage of the flood during its progression and decrease. Resulting data and images have been useful in planning the emergency measures and in assessing flood damage. RADARSAT has also the ability to characterize hydrological properties of watersheds. It has been used in agricultural catchments in Europe for mapping soil surface roughness, which affects runoff coefficients, concentration time and resistance to erosion processes. Used to complement optical data, RADARSAT has provided information on the status of land use and soil protective cover in drainage basins. This information can then be translated into parameters and coefficients that hydrological models can use for runoff and flood forecasting     

Partitioning and Speciation of Trace Metal Diagenesis in Differing Depositional Environments in the Sediments of the Oman Margin

Organic-rich sediment samples collected from a transect within, and below, the Oman Margin oxygen minimum zone (OMZ) were analysed using a sequential leaching technique to characterise the diagenetic behaviour and speciation of Mn and Fe in operationally defined sediment host fractions. Trace metals showed distinct diagenetic behaviour in the two contrasting environments that were sampled. The absence of non-detrital Mn in the cores below the OMZ site is attributed to the lack of easily reducible oxides in surficial sediments and to the reduction and export of any moderately reducible aged oxides. The reactive form of solid phase Mn showed a classic feature of enrichment in the upper layer of the sediments at the abyssal site, reflecting the presence of an oxidising sedimentary layer which acts as a Mn trap during its recycling. The diagenetic Mn enrichment was inferred from typical downcore colour changes and an upward-increasing Mn content in the upper core sections. An easily reducible Fe oxide layer was observed in the abyssal sediments at an identical depth to the Mn enrichment suggesting that Fe associated with Mn oxides also has undergone sub-oxic diagenesis. However, the association of Fe with organic matter did not indicate diagenetic modification; i.e., the binding strength of the metal with organic materials appears to be sufficiently strong to preserve the trace metal. The speciation signature of non-detrital Fe differed from that of Mn. The association of Fe with organic matter suggests that this metal does not undergo diagenetic modification and is preserved in abyssal sediments. The contrasting behaviour of Mn and Fe observed between cores within the OMZ were particularly interesting. Another interesting observation was that, for cores below the OMZ, the iron oxides were associated with the Mn-oxide peak, rather than deeper in the sediments as observed by earlier studies in the Atlantic [Froelich et al. (1979). Geochim. et Cosmochim Acta 43, 1075–1090].This revised version was published online in May 2005 with corrections to the article title.     

The problem of the Precambrian basement in Rajasthan,western India

The Banded Gneissic Complex (BGC) of Rajasthan, considered to form the basement underlying the Precambrian (Proterozoic) Aravalli metasediments, shows an erosion surface marked by a conglomerate and an angular unconformity, with gneissic foliation crossing the metasedimentary bands at only a few places. The BGC is a composite gneiss, evolved by extensive migmatization of metasedimentary rocks of diverse composition, and possibly metaigneous rocks. The contact between the BGC and the Aravalli rocks is a gently curved surface, whereas the gneissic foliation, as well as the large-scale metasedimentary enclaves within the gneissic complex, show all the intricate patterns of super-imposed folding traceable in the Aravalli rocks. This implies that the “basement” gneisses have been involved in ductile deformation with the Aravalli rocks, the migmatization being synkinematic with the first deformation in the latter. All these apparently conflicting lines of evidence can be resolved if the gneisses, as we see them now, represent not the original, but the mobilized basement, with the BGC-Aravalli boundary representing, for a large part, a migmatite front, rather than the original basement-cover interface. Only at a few places was there a chance of the original basement escaping mobilization and thus, little chance of identifying this original interface.     

Spectropolarimetry of comets Austin and Churyumov-Gerasimenko

Spectropolarimetric observations from 5000 to 8000 Å have been obtained for comets P/Austin (1982g) and P/Churyumov-Gerasimenko (1982f). The observations were spaced over phase angles of 50–125° for comet Austin and 10–40° for comet Churyumov-Gerasimenko. The use of spectropolarimetry allowed an evaluation of continuum polarization without molecular line contamination. Especially for comet Churyumov-Gerasimenko, the curve of polarization versus phase angle resembles curves for asteroids, where the polarization is negative (electric vector maximum parallel to the scattering plane) for phase angles less than 20° and the most negative polarization is from ?1 to ?2%. The negative polarization at backscattering angles may be due to multiple scattering in agglomerated grains, as assumed for asteroids, or to Mie scattering by small dielectric particles. If multiple scattering is important in comet dust, polarization measurements may imply a low albedo, less than 0.08. The polarization of comet Austin remained steady during a large change in the dust production rate. Both comets increased continuum flux by a factor of 2 near perihelion. The continuum of comet Churyumov-Gerasimenko had the shape of the solar spectrum with derivations less than 5%. The equivalent width of spectral features of C₂, NH₂, and O varied as r^?2.     

The magnetic configuration of the November 18, 1968 loop prominence system

Computed current-free magnetic fields are compared to the loop prominence associated with the west limb proton flare of 18 November 1968. Successive sets of fitting fieldlines closely resemble the loop prominence system throughout its growth and lifetime. The successive position bases of the fieldlines reproduce the drift rate of spreading two-ribbon flares.     

The wind-speed measurement capability of spaceborne radar altimeters

This study represents an attempt to quantitatively assess the capability of a spaceborne radar altimeter to infer ocean surface wind speeds from a measurement of the backscattered power at vertical incidence. The study uses data acquired during 184 near overflights of NOAA data buoys with the GEOS-3 satellite radar altimeter and encompasses a wind-speed range from less than 1 to 18 m/s. An algorithm is derived from the data comparison for converting measurements of the normalized scattering cross section of the ocean surface at 13.9 GHz into estimates of the surface wind speed at the standard anemometer height of 10 m. The algorithm is straightforward and potentially useful for on-board processing of raw altimeter data for the purpose of providing real-time estimates of surface wind speed. For winds in the range of 1 to 18 m/s, the mean difference between the altimeter-inferred winds and the buoy measurements is negligible while the standard deviation of the difference is 1.74 m/s.     

Studies in the application of recurrence relations to special perturbation methods

Using the rectangular equations of motion for the restricted three-body problem a comparison is made of the integration of these equations by the Encke method and by a set of perturbational equations. Each set of differential equations is integrated using Taylor series expansions where the coefficients of the powers of time are determined by recurrence relations. It is shown that for very small perturbations the use of the perturbational equations is more efficient than the use of the Encke method. A discussion is also given of when Cowell's method is more efficient than either of these techniques.     

Luni-solar perturbations of an Earth satellite

Luni-solar perturbations of the orbit of an artificial Earth satellite are given by modifying the analytical theory of an artificial lunar satellite derived by the author in recent papers. Expressions for the first-order changes, both secular and periodic, in the elements of the geocentric Keplerian orbit of the earth satellite are given, the moon's geocentric orbit, including solar perturbations in it, being found by using Brown's lunar theory.The effects of Sun and Moon on the satellite orbit are described to a high order of accuracy so that the theory may be used for distant earth satellites.     

Contents of Volume 47

Volume Contents

Contents of Volume 47