The scenario is an intriguing one: An airplane flying over a remote stretch of ocean launches a cylindrical container attached to a parachute. Once it hits the surface of the water, the hinged container opens and releases a 3-foot-long multisensor probe equipped with sophisticated electronic instrumentation. As the microcomputer-controlled probe descends to the ocean bottom, aided by a small anchor, it takes readings of various environmental conditions such as temperature and salinity (or conductivity) at various depths and stores the data on memory chips. Once on the bottom, it continues to take a timed series of preprogrammed measurements as it phases in and out of a "sleep" mode to conserve battery power. At a pre-designated time -- or when triggered by a certain reading -- the probe detaches from its anchor and rises to the surface, taking yet another series of measurements on the way up. After surfacing, the recorded information is transmitted by telemetry to an ARGOS satellite that relays the information to a land-based station. That is one possible application for the Autonomous Environmental Sentinel (AES) developed by scientists at Battelle Memorial Institute. However, most early uses of the probe -- which can be deployed from boats and submersibles, as well as aircraft -- are likely to involve near-shore monitoring of discharges from wastewater-treatment plants or industrial discharges of chemical pollutants. In near-shore applications, the probes could be recovered manually and the data downloaded via a communications port on the device. To aid recovery, it would be outfitted with a xenon flasher and RF transmitter that activate upon surfacing. The precise configuration of an AES will depend on the application, notes Brad DeRoos, an ocean scientist at Battelle who served as project manager for development of the environmental sentinel. Near-shore applications wouldn't need the satellite transmission capability, since it will be more economical to physically recover the probes and then reuse them. However, for remote applications -- in the Antarctic Ocean, for example -- the cost of recovery might be prohibitive. Development and proof-of-concept work began in 1991 in partnership with Ocean Sensors Inc., a San Diego instrument manufacturer that is a co-holder of the patent on the technology. The original objective was to develop an instrument for oceanographic studies, DeRoos notes. "But we began getting a lot of calls from people interested in using the technology for environmental monitoring. So we took a little different twist and adapted it for near-shore applications." New types of sensors were added to increase versatility, and designers made sure the device would accommodate other types of sensors for applications such as detecting heavy metals. In its current configuration, the AES can operate for up to two months at a time at depths up to 1,000 feet. More advanced batteries could extend deployment times to as long as a year. For certain environmental applications, the AES could be programmed to detect specific toxic chemicals and, when a reading exceeds a predetermined parameter -- indicating an illegal discharge -- disengage from its anchor, rise to the surface, and then use the RF transmitter to alert regulatory authorities. An electrochemical method -- using a 9-volt current to corrode and dissolve the stainless steel connecting wire -- is employed to release the anchor. The primary engineering challenge in developing the AES was that of finding a way to pack all the necessary electronics into a 2 3/4 -in.-diameter tube so that it would fit into the aircraft-based launcher, yet still ensure that the probe would have enough buoyancy to float back to the surface. "We had to optimize the weight everywhere we could," DeRoos says.