Rising sea level has important humanitarian and economic implications. Scientists are rigorously investigating the contribution of glacial ice sheets to sea-level rise. Knowledge of the mass balance of the ice sheets is important in understanding their dynamics. The accumulation rate of snow on ice sheets is an important variable in determining this mass balance. The accumulation rate is currently determined using ice cores and pits. This is a tedious method to obtain coverage over the entire ice sheet due to the limited number of samples that can be acquired. The only practical means of obtaining coverage over a large area would be by means of remote sensing. We have developed a wideband radar to map the isochronous layers in the ice sheet This will help reduce the uncertainty associated with sparse sampling of the ice sheet. We built a compact FM-CW radar that operates from 500 to 2000 MHz with range resolution of about 10 cm. Both the transmitter and receiver were housed in a single Compact PCI chassis. We used a YIG oscillator to generate the FM signal. The performance of an FM-CW is usually degraded by the nonlinearity of the source. We linearized the sweep of the YIG oscillator by means of a phase-locked loop (PLL). We have successfully tested the radar in the lab and we will be performing tests during the 2004 summer field experiments at the Summit camp in Greenland. We successfully tested a connectorized version of this radar during the 2003 field experiments at the North Greenland Ice Core Project (NGRIP) camp. We were able to map the internal layers up to a depth of about 150 m over a 5-km transect. We also conducted detailed snow pit studies at several spots over the transect for correlating the visually determined layers with the radar determined layers. We will present the radar design, laboratory test results of its performance, results from the experiments at Summit and a comparison of the radar data with information derived from ice cores and snow pits.

Testable design of unilateral iterative logic arrays (ILA) of combinational cells under the assumption of a single cell failure is considered. The concepts of one-step testability and one-step C-testability are introduced. Methods to modify the basic cell flow table so as to facilitate fault detection and location are given. It is shown that if no directly observable outputs from each cell are available, then it is possible to augment the cell flow table by the addition of a fixed number (≤4) of columns and a row so that a faulty cell can be located by a test of length proportional to log2p, where p is the number of cells in the array. However, if directly observable outputs are available from each cell, then the test length is shown to be independent of the array length to locate a faulty cell.