Concurrent Use of OSCAT and AltiKa to Characterize Antarctic Ice Surface Features

Radar altimetry provides an important geophysical parameter, backscatter coefficient (σ₀), which is useful in studying target surface characteristics. Ku-band (Oceansat-2 scatterometer- OSCAT) and Ka-band (SARAL-AltiKa altimeter) data are concurrently used to characterize polar surface features over the Antarctic region. Maximum-likelihood classification has been employed to classify combined data set (AltiKa and OSCAT) for discrimination among sea ice, open water, and ice sheet (interior and exterior). The sea ice region obtained using the current approach has been compared with sea ice boundary derived from passive microwave data.     

Population synthesis of cataclysmic variable star: I. A new methodology and initial study on the post common-envelope stage

We report the results of our population synthesis for post common-envelope binaries by following the evolution of each system in detail. Our main focus is a comparison with the white dwarf mass distribution of post common-envelope systems from the Sloan Digital Sky Survey. We employ a Monte Carlo method to choose the initial parameters of the progenitors (primary mass, mass ratio and orbital period). Then the evolution of the progenitor binary system is followed up to the onset of the common-envelope phase, which usually occurs near the tip of the giant branch or asymptotic giant branch. An approximate post-Helium flash evolution for primary masses ${\leq}2.25 \mathrm{M_{\odot}}$ is included. The binary parameters before and after common-envelope phase are calculated using the energy budget argument. In this paper we address the case of α _CE=1.0, which is the commonly adopted value to calculate the common-envelope ejection. We consider a hydrogen-exhausted core to define the core mass of the primary (white dwarf mass, M _WD) at the onset of common envelope phase. To obtain the present-day M _WD distributions, we assumed a constant star formation rate. The distribution resulting from our population synthesis shows a double peak profile for M _WD, similar to previous population syntheses and recent observational data. Our present synthesis result could not reproduce the location of the low and high mass peaks from the observations, but shows how a future synthesis can be made to produce an M _WD distribution which is closer to observational data.     

Quantification of improvements by using AWiFS over WiFS data

The Advanced WiFS sensor of RESOURCESAT- 1 satellite offers significantly improved specifications compared to the WiFS sensor onboard IRS IC, P3 and ID satellites. The improvements are in terms of spatial resolution, radiometry (quantisation levels) and number of spectral bands. In the present study, an attempt has been made to quantify the gains due to these enhanced specifications. The study has been carried out in a predominantly agricultural area. For the study reported here, one set of overlapping data acquired on the same day by WiFS and AWiFS sensors has been selected. This eliminates the need of atmospheric correction/ normalization for comparison. The effect of spatial resolution has been studied by applying ISODATA spectral clustering algorithm with number of clusters set at three different levels, viz., 10, 20 and 30. They are assumed to mimic first, second and third level classification, respectively. Output images were filtered using 3 × 3 majority filter. Homogeneous polygons having area less than 1/2 and 1 pixel of WiFS were recorded. This indicates the minimum loss by using WiFS data. A relative gain of 10 – 15 % is observed due to improvement in spatial resolution. For comparison of radiometry, local variance measure was used. It was observed that local variance is much larger for AWiFS data in comparison with WiFS data. This indicates presence of enhanced local contrast, hence heterogeneity, in AWiFS data over WiFS data. Separability analysis has been carried out to demonstrate improvements due to two additional spectral bands (Green and SWIR).     

Radio frequency interference measurements in Indonesia

We report the first measurements of radio frequency spectrum occupancy performed at sites aimed to host the future radio astronomy observatory in Indonesia. The survey is intended to obtain the radio frequency interference (RFI) environment in a spectral range from low frequency 10 MHz up to 8 GHz. The measurements permit the identification of the spectral occupancy over those selected sites in reference to the allocated radio spectrum in Indonesia. The sites are in close proximity to Australia, the future host of Square Kilometre Array (SKA) at low frequency. Therefore, the survey was deliberately made to approximately adhere the SKA protocol for RFI measurements, but with lower sensitivity. The RFI environment at Bosscha Observatory in Lembang was also measured for comparison. Within the sensitivity limit of the measurement equipment, it is found that a location called Fatumonas in the surrounding of Mount Timau in West Timor has very low level of RFI, with a total spectrum occupancy in this measured frequency range being about 1 %, mostly found at low frequency below 20 MHz. More detailed measurements as well as a strategy for a radio quiet zone must be implemented in the near future.