From: Jim Ray Subject: [IGSMAIL-2150] work near USNO antenna Date: Tue, 9 Feb 1999 7:19:29 PST ****************************************************************************** IGS Electronic Mail Tue Feb 9 7:19:29 PST 1999 Message Number 2150 ****************************************************************************** Author: Jim Ray Subject: work near USNO antenna A large piece of air-handling mechanical equipment was lifted onto the rooftop of Bldg 52 near the USNO GPS antenna this morning, 09 February 1999. The air-handler passed above the horizon of the antenna although not directly over it. It is very possible that observations were affected by this work. Even worse, though, the air-handler was placed only a short distance from the antenna on a raised platform area. The separation between the antenna and air-handler is about 12.8 meters. Below is a schematic of the new geometry: <- approx. North ____________ | | | Air- | 1.6 m | handler | Ant. | | == ^ --------------------- || 1 m 0.7 m | | || | |__________________________|| v | <------------- 12.8 m ----------> [Southeast corner area of USNO Bldg 52 rooftop] As of today, the top of the metal air-handler rises about 1.3 meters above the choke-ring antenna. At a distance of 12.8 meters, the structure is only about 6 degrees above the antenna horizon. However, the potential for multipath problems is presumably great. I have only recently learned that during the course of related work on the rooftop over the last couple of months (since December 1998 at least) significant amounts of sheet metal and other metal pieces have been moved around the rooftop near the GPS antenna. We will try to determine the possible impact of these activities on the quality of the USNO observations. If significant degradation is detected, the antenna may need to be relocated. We apologize for the short notice and inconvenience to users. ========================================================================= Jim Ray e-mail: jimr@maia.usno.navy.mil U.S. Naval Observatory, EO Dept. phone : 202-762-1444 3450 Massachusetts Avenue, NW fax : 202-762-1563 Washington, DC 20392-5420 ========================================================================= [Mailed From: Jim Ray (USNO 202-762-1444) ]