Janet Rountree

Criteria for the spectral classification of B stars in the ultraviolet

A set of criteria has been developed for the classification of B stars from ultraviolet spectra alone, using MK standards drawn from the optical region. The observational material consists of archival high-dispersion spectra obtained by the SWP camera on the IUE spacecraft. The spectra were resampled to a resolution of 0.25 A, normalized, and plotted on a uniform scale of 10 A cm -1 . Approximately 100 stars having normal MK spectral types in the range B0-B8, III-V, have been classified.

Scan-based processing with JPEG 2000

Many space-borne remote sensing missions are based on scanning sensors that create images a few lines at a time. Moreover, spacecraft typically have limited amounts of available memory, on account of weight, size and power constraints. For these reasons, the JPEG-2000 emerging standard has a requirement for stripe processing in order to meet the needs of the remote sensing profile. This paper first briefly presents the JPEG- 2000 algorithm, highlighting details pertinent to scan-based processing. A technique for meeting the stripe processing requirement is then presented. This technique use a sliding window rate control mechanism that maintains the desired average bit rate over entire images, while retaining a minimum number of bytes in memory at any given time. Results are then presented to show performance over various sliding window sizes.

Reduced memory multi-layer multi-component rate allocation for JPEG2000

Remote sensing images are often multispectral in nature and are acquired by on-board sensors in a “push-broom” fashion. These images are compressed and transmitted to ground stations for further analysis. Since they are extremely large, buffering all acquired data before encoding requires huge amounts of memory and introduces latency. Incremental compression schemes work on small chunks of raw data as soon as they are acquired and help reduce buffer memory requirements. However, incremental processing leads to large variations in quality across the reconstructed image. We propose two “leaky bucket” rate control algorithms that can be employed for incrementally compressing hyperspectral images using JPEG2000. Both schemes perform rate control using the fine granularity afforded by JPEG2000. The proposed algorithms have low memory requirements and enable SNR scalability through the use of quality layers. Experiments show that the proposed schemes provide significant reduction in quality variation with no loss in mean overall PSNR performance.

Scan-based implementation of JPEG 2000 extensions

JPEG 2000 Part 2 (extensions) contains a number of technologies that are of potential interest in remote sensing applications. These include arbitrary wavelet transforms, techniques to limit boundary artifacts in tiles, multiple component transforms, and trellis-coded quantization (TCQ). We are investigating the addition of these features to the low-memory (scan-based) implementation of JPEG 2000 Part 1. A scan-based implementation of TCQ has been realized and tested, with a very small performance loss as compared with the full image (frame-based) version. A proposed amendment to JPEG 2000 Part 2 will effect the syntax changes required to make scan-based TCQ compatible with the standard.

Be Stars in the Ultraviolet Spectral Classification System

Rountree and Sonneborn (1991) developed a system for the classification of ultraviolet B-star spectra, using MK standards drawn from the optical region. The observational material consisted of high-dispersion spectra obtained with the Short Wavelength Prime (SWP) camera on the International Ultraviolet Explorer (IUE) spacecraft. The classification criteria were based exclusively on photospheric absorption lines, primarily lines of C III, Si II, and Si III. The stellar wind lines of Si IV, C IV, and N V were not used in the classification.