Geodetic imaging with airborne LiDAR: the Earth's surface revealed.

The past decade has seen an explosive increase in the number of peer reviewed papers reporting new scientific findings in geomorphology (including fans, channels, floodplains and landscape evolution), geologic mapping, tectonics and faulting, coastal processes, lava flows, hydrology (especially snow and runoff routing), glaciers and geo-archaeology. A common genesis of such findings is often newly available decimeter resolution 'bare Earth' geodetic images, derived from airborne laser swath mapping, a.k.a. airborne LiDAR, observations. In this paper we trace nearly a half century of advances in geodetic science made possible by space age technology, such as the invention of short-pulse-length high-pulse-rate lasers, solid state inertial measurement units, chip-based high speed electronics and the GPS satellite navigation system, that today make it possible to map hundreds of square kilometers of terrain in hours, even in areas covered with dense vegetation or shallow water. To illustrate the impact of the LiDAR observations we present examples of geodetic images that are not only stunning to the eye, but help researchers to develop quantitative models explaining how terrain evolved to its present form, and how it will likely change with time. Airborne LiDAR technology continues to develop quickly, promising ever more scientific discoveries in the years ahead.

Haematopoietic malignancies in zoo animals.

Myelogenous leukaemia was found in a Russell's viper, a Honduran milk snake, a marine toad, a Byrne's marsupial mouse and an African hedgehog. Lymphocytic leukaemia was present in a broad banded copperhead and an Indian lion. Visceral lymphomatosis was observed in a snowy owl.

Polar motion measurements: subdecimeter accuracy verified by intercomparison.

An important bound on the accuracy of modern techniques for monitoring polar motion is established by intercomparison of measurement series from two different observing techniques, very long baseline interferometry and satellite laser ranging. The root-mean-square differences between the estimates of the pole position from both techniques are shown to be only 2 milliseconds of arc (about 6 centimeters at one Earth radius). In the absence of common systematic errors, these differences bound the total errors in both sets of estimates. An initial investigation did not reveal any clear signature in the pole position that seems to be associated with major earthquakes. Continued measurements at this level of accuracy hold promise for resolving long-standing arguments over such questions as the nature of the excitation mechanism required to maintain the motion of the pole.

Variations in the rotation of the Earth.

Variations in the earth's rotation (UT1) and length of day have been tracked at the submillisecond level by astronomical radio interferometry and laser ranging to the LAGEOS satellite. Three years of regular measurements reveal complex patterns of variations including UT1 fluctuations as large as 5 milliseconds in a few weeks. Comparison of the observed changes in length of day with variations in the global atmospheric angular momentum indicates that the dominant cause of changes in the earth's spin rate, on time scales from a week to several years, is the exchange of angular momentum between the atmosphere and the mantle. The unusually intense El Niño of 1982-1983 was marked by a strong peak in the length of day.

Restabilization with methadone after methadyl acetate maintenance.

Sixty-eight heroin addicts maintained for 40 weeks on a regimen of methadyl acetate or methadone hydrochloride in a double-blind study were transferred to a uniform dose of 60 mg of methadone daily at the end of their tenure in the study. They were observed for the ensuing six weeks, during which their daily methadone doses were adjusted according to their clinical needs. Patients were observed for symptoms and signs of discomfort and for the amount of illicit drug use during this period of transition. The results indicate that patients maintained on a regimen of methadyl acetate can be readily restabilized with methadone and that sudden decrease of the methadone dose tends to result in the patient's supplementing with illicit heroin. Conversely, increasing methadone doses resulted in a corresponding reduction in illicit drug use. It is suggested that a chronic covert abstinence syndrome may exist in some patients receiving long-term methadone maintenance therapy, and that while it may contribute to their continued illicit drug use, it may have a different pathophysiologic basis and require different therapeutic considerations.

Earth rotation measured by lunar laser ranging.

The estimated median accuracy of 194 single-day determinations of the earth's angular position in space is 0.7 millisecond (0.01 arc second). Comparison with classical astronomical results gives agreement to about the expected 2-millisecond uncertainty of the 5-day averages obtained by the Bureau International de l'Heure. Little evidence for very rapid variations in the earth's rotation is present in the data.