Hybrid optical processing of sea surface imagery for the estimation of wave parameters

With the availability of high spatial resolution space-borne sensors, the wave parameters like wave propagation direction, wavelength of the dominant wave etc., are estimated from the Fourier spectra of ocean scene imageries. The hybrid optical processor is the most suitable for the analysis of imageries, since it utilises the parallel processing capability of the optical processor for generating the Fourier spectra. An attempt has been made to use a hybrid processor with wedge-ring sampling detector array for the estimation of wave parameters and the results are encouraging.     

Oil slick identification from imageries using optical power spectra

A new method for semi-automatic identification of oil slick on ocean/sea surface from space borne imagery using optical power spectra has been suggested. This method is based on the fact that the presence of the oil slick in the ocean suppresses the normal wave pattern that will be present in the ocean area without oil slick and the power spectra of the image area having the oil slick will be devoid of the peak corresponding to the dominant wave. In addition, the general shape of the oil slick will increase the low frequency content in the power spectra. The method has been applied for test areas containing oil slicks and the results are encouraging.     

On the irradiation history and origin of gas-rich meteorites

With the transmission electron microscope, we have made detailed studies of the track density gradients and irradiation geometries of track-rich grains and chondrules in sections of Fayetteville and Kapoeta. We have made the same type of studies in sections of lunar breccias and grains from lunar soil for comparison.A substantial fraction (50–90 per cent) of the meteoritic track-rich grains and chondrules show evidence of having been irradiated anisotropically in their different faces, as would be expected for irradiation on the surface of a parent body. Our observations thus support the hypothesis that the irradiation of these grains and chondrules took place on the regoliths of asteroidal-sized bodies.Measurement of steepest track density gradients indicate that while there are finite differences between spectra exhibited by individual gas-rich meteorites, the average solar flare spectral shapes have been similar over the last ~4 b.y. or so.     

Hydrocarbon Vapor Diffusion in Intact Core Sleeves

The diffusion of 2,2,4-trimethylpentane (TMP) and 2,2,5-trimethylhexane (TMH) vapors put of residually contaminated sandy soil from the U.S. Environmental Protection Agency (EPA) field research site at Traverse City, Michigan, was measured and modeled. The headspace of an intact core sleeve sample was swept with nitrogen gas to simulate the diffusive release of hydrocarbon vapors from residual aviation gasoline in and immediately above the capillary fringe to a soil-venting air flow in the unsaturated zone. The resulting steady-state profile was modeled using existing diffusivity and air porosity estimates in a balance of diffusive flux and a first order source term. The source strength, which was calibrated with the observed flux of 2,2,4-TMP leaving the sleeve, varied with the residual gasoline remaining in the core, but was independent of the headspace sweep flow rate. This finding suggested that lower soil-venting air flow rates were in principle as effective as higher air flow rates in venting LNAPL vapors from contaminated soils. The saturated vapor concentration ratio of 2,2,4-TMP to 2,2,5-TMH decreased from 6.6 to 3.5 over the duration of the experiments in an expression of distillation effects. The vertical profile model was tested against sample port data in four separate experiments for both species, yielding mean errors ranging from 0 to—24 percent in magnitude.     

Photometric study of distant open clusters in the second quadrant: NGC 7245, King 9, King 13 and IC 166

We present a UBV CCD photometric study of four open clusters, NGC 7245, King 9, IC 166 and King 13, located between   l = 90°  and 135°. All are embedded in a rich Galactic field. NGC 7245 and King 9 are close together in the sky and have similar reddenings. The distances and ages are: NGC 7245, 3.8 ± 0.35 kpc and 400 Myr; King 9 (the most distant cluster in this quadrant), 7.9 ± 1.1 kpc and 3.0 Gyr. King 13 is 3.1 ± 0.3 kpc distant and 300 Myr old. King 9 and IC 166 (4.8 ± 0.5 kpc distant and 1 Gyr old) may be metal-poor clusters  ( Z = 0.008)  , as estimated from isochrone fitting. The average value of the distance of young clusters from the Galactic plane in the above longitude range and beyond 2 kpc (−47 ± 16 pc, for 64 clusters) indicates that the young disc bends towards the southern latitudes.     

A cold pool formation in the Lakshadweep Sea during Indian summer monsoon

In Lakshadweep Sea, the distribution of observed sea surface temperature (SST) during summer monsoon season (June–September) shows the presence of a distinct cold pool (SST?<?27°C). Available satellite measurements and assimilated datasets are utilized to investigate the characteristics and mechanisms that govern the genesis and evolution of this cold pool. It is located in the grid 8° N–10° N/74° E–76° E, with a diameter of about 200?km, centered approximately at 9° N/75° E off the southwest coast of India. This cold pool, which we call as the Lakshadweep cold pool (LCP), forms invariably during the fifth pentad of June as a small cooling within the cold surface waters advected northward along the southwest coast of India from the Arabian Sea Mini Cold Pool. With the progress of the season, LCP intensifies, spread radially outwards and shows a westward spread during late July. Maximum intensity and radial spread are attained during July. By the end of August, LCP extends northward along the coast up to 13° N, and by September, it gets completely dissipated. Within the LCP, the thermocline exhibits pronounced shoaling compared to the adjacent regions. The intensity, duration, and spread of LCP showed annual variations in each summer monsoon during 1998–2005 and owes its origin to upwelling produced by uplift of poleward undercurrent induced by an elevated bathymetry in the presence of a seamount. The mechanism for the intensification is thought to be due to the combined action of Ekman pumping due to positive wind stress curl, eddy-induced upwelling due to the Lakshadweep low, and the intensification of the poleward undercurrent during the season. West- and northward spreads of LCP are attributed to the westward movement of Lakshadweep Low and the northerly spreading and intensification of positive wind stress curl, respectively. The mechanisms that govern this phenomenon are thoroughly examined.     

Fission track studies of xenolithic chondrites: implications regarding brecciation and metamorphism

We have studied fission tracks in phosphates from one gas-poor chondrite and three gas-rich chondrites to determine their thermal history and brecciation time scales. More than 70 percent of the tracks in whitlockites in these meteorites are due to the decay of extinct Pu²⁴⁴.Whitlockites separated from Bhola, a gas-poor chondrite, have $\text{ρ}{}_{\mathrm{Pu}}\text{ρ}{}_{\mathrm{U}}\text{= 2.6–5.2}$ and a model fission track age of 4.0 Gyr for a $\text{(}\text{Pu}\text{U}\text{)}{}_{\mathrm{4.55Gyr}}\text{= 0.045}$. Brecciation of the Bhola meteorite must have occurred at ?4.3 Gyr to account for the metal data (Scott and Rajan, 1981). A minimum cooling rate of $\text{0.9}{}_{\mathrm{–0.2}}{}^{0.3}\text{K}\text{Myr}$ in the temperature interval 800 to 300 K obtained from the track data is a factor of seven higher than the metallographic cooling rate ($\text{0.1}\text{K}\text{Myr}$).For the gas-rich chondrites, the $\text{ρ}{}_{\mathrm{Pu}}\text{ρ}{}_{\mathrm{U}}$ in whitlockites are: Weston, 32–148; Fayetteville, 21–227; and St. Mesmin, 26–137. Whitlockites from all these meteorites give model fission track ages of 4.4 Gyr assuming a $\text{(}\text{Pu}\text{U}\text{)}{}_{\mathrm{4.55\; Gyr}}\text{= 0.045}$. The final brecciation event definitely did not reset the track clock in phosphates of St. Mesmin. Our data suggest that it is also true for Weston and Fayetteville. We conclude that our observed fission track ages date the end of metamorphic cooling in the meteorite parent bodies and support the planetesimal model for the formation of xenolithic chondrites.