Mobile Facility Completes First Test at Sea
In mid-June, the second ARM Mobile Facility, or AMF2, faced its first test on the open seas off the coast of Cape Cod, Massachusetts. Led by Rich Coulter, AMF2 co-manager from Argonne National Laboratory, the AMF2 team installed a subset of AMF2 instruments on the RV Connecticut to test their operation in a marine environment and to experience the potential problems likely to be encountered during a long-term shipboard deployment.
One primary objective of the testing was to evaluate the control software for the new AMF2 stable platform, as well as to evaluate the operation of various instruments in stabilized and non-stabilized modes. Logistics and planning support for the test was provided by Woods Hole Oceanographic Institute.
- Day 1 included loading and installing all the instruments and data systems onto the ship.
- Day 2 comprised a “day cruise” to perform initial tests of the stable platform and data communications, with the ship turning in various, predetermined directions and returning to dock for the night.
- Days 3 and 4 took the team on an overnight voyage, sailing parallel to the East Coast. These data will allow the team to evaluate system operations in differing sea states, orientations, and sun angles.
- On day five, the last day, the ship returned to port, where the team offloaded and packed up all the instruments and equipment for return to Argonne.
“Overall, we did everything we wanted to do; I think the test was extremely successful,” said Coulter. “We learned a lot and will make adjustments that should help us immensely when we deploy the complete facility.”
Key Components for the Marine Mobile Facility
Designed for deployment flexibility—particularly for obtaining atmospheric data over the ocean—the AMF2 consists of a number of separate instrument modules containing one or more instruments and their supporting electronics systems. The modules—climate controlled and built of stainless steel—can be deployed together or separately, with wireless data communications.
Wireless communications will significantly reduce the infrastructure congestion and setup time for the facility. Strategically placed radio frequency antennas eliminate the need for cables to connect the instruments to the data collection system, which is a “mini” ARM data system. However, the heart of the AMF2 marine capability is a small, innocuous-looking box called the IMU, or inertial measurement unit.
The IMU, located near the center of the ship, records the exact longitude, latitude, and motion (pitch, roll, speed, surge, sway, etc.) of the ship every 0.02 seconds. A global positioning system (GPS), located conveniently within sight of satellites, is part of the system. Combined data from the IMU and GPS will be used to provide a “ship disposition” datastream containing the needed correction information to adjust for these motion variables in several critical instrument measurements that rely on vertical-pointing and air motion data.
Another key component for AMF2 shipboard deployments is the stable platform, which moves in opposition to the ship’s movement—if the ship tilts in one direction, the platform is programmed to tilt in the opposite direction. Control software uses information from the IMU to keep the platform level and in the correct orientation.
The stabilized platform can support a relatively large payload—several hundred pounds. In general, the instruments placed on the platform require shading from the sun or need to point vertically. During the testing in June, the platform hosted a microwave radiometer and a multifilter rotating shadowband radiometer, as shown in this video; a total sky imager was added to the platform later.
Other instruments deployed throughout the ship included a micropulse lidar, upward and downward looking infrared thermometers, and two non-standard ARM instruments that do not require stabilization: a portable radiation package and another radiometer to measure total and diffuse radiation.
In October, the AMF2 begins its first official deployment at Steamboat Springs, Colorado, for the STORMVEX field campaign. Though land-based, the six-month STORMVEX campaign provides an excellent initial deployment for gauging the robustness and modularity of the instruments. Several modules will be deployed about halfway up the mountain at an elevation of about 2700 meters, and other modules will be located on the valley floor.