currents within the IIP current file. They were 

 compiled by CUP from various sources 

 constituting a much lower quality data base then 

 that used for the first region. 



Contained in Appendix A is a hsting of the 1979 

 IIP current file. The current direction in degrees 

 true and the speed in cm/ s (51 cm/ s = 1 knot) are 

 listed for every 20 "minutes of latitude and 

 longitude except in the vicinity of the Labrador 

 Current where the longitude spacing is 10 minutes. 

 This finer grid encompasses all of region 1 and a 

 small part of region 2. Region 1 currents in Appen- 

 dix A are indicated by asterisks (*). There was only 

 one current file for the entire 1979 season as 

 opposed to four files which were previously used, 

 one each for April, May, June and July. It was felt 

 that monthly variation of currents within a given 

 season was not large enough to warrant more than 

 one IIP current file. 



SATELLITE TRACKED BUOYS 



The Oceanographic Unit began examining the 

 feasibility of using satellite tracked drifting buoys 

 to measure currents as early as 1975. In 1976, 

 1977, and 1978 satellite tracked buoy transmitting 

 terminals (BTT's) were deployed in the Ice Patrol 

 area and tracked using the NIMBUS-6 satellite 

 system. Positions obtained were analyzed to deter- 

 mine currents. The results of these tests were so 

 successful that the Oceanographic Unit presented 

 a position paper at the 1978 IIP Planning Con- 

 ference stating that BTT's could replace standard 

 oceanographic surveys as the method for gather- 

 ing current information to evaluate the IIP cur- 

 rents. This idea was accepted by CUP and 1979 

 became the first season since 1948 during which no 

 oceanographic surveys were made by a Coast 

 Guard vessel in support of IIP operations. 



The satellite system used during the 1979 Ice 

 Patrol season was TIROS-N. When the satellite is 

 within sight of a BTT it records the data being 

 transmitted on 416.65 MHz. This information is 

 processed and encoded by the TIROS information 

 processor and retransmitted almost instantane- 

 ously on the spacecraft beacon frequency, 136.77 

 MHz. The ground receiving station and the BTT 

 must both be within line of sight of the satellite for 

 this retransmission to be received at the ground 

 station. In the fall of 1978 a prototype Local User 

 Terminal (LUT) was established at the 

 Oceanographic Unit to allow relatively independ- 

 ent and near real-time data reception. It is capable 

 of receiving the transmissions of both the 



NIMBUS-6 and TIROS-N satellites and processing 

 them to obtain position and sensor data. With its 

 present location in Washington, D.C., in the 

 TIROS-N mode the LUT normally receives infor- 

 mation from 2 satellite passes daily with the 

 capability of locating BTT's anywhere within the 

 IIP area. The maximum accuracy of the system 

 with the incorporation of adequate reference 

 beacons is about ±3 km (1.6 nautical miles). 



The cornerstone of the new current measuring 

 scheme is the BTT's themselves. All BTT's used 

 are in what is called the TIROS Oceanographic 

 Drifter (TOD) configuration (Figure 1). This 

 includes the basic buoy, window shade drogue, the 

 drogue sensor, temperature sensor and battery 

 monitor. The drogue extends from about 12 to 24 

 m below the sea surface and is designed to reduce 

 buoy leeway as much as possible. The temperature 

 sensor is accurate to within + 1.0°C and provides 

 valuable sea surface temperature data. During the 

 1979 season all BTT's were air deployed from 

 Coast Guard HC-130 aircraft (although they can be 

 ship deployed) utilizing a special air deployment 

 package (Figures 1 and 2). The system is designed 

 so that the BTT on a pallet is slid out the rear cargo 

 door of the aircraft and parachutes to the sea 

 surface. Water-activated explosive cutters cut 

 away the parachute, and the specially designed 

 hardware connecting the pallet to the BTT 

 dissolves causing the pallet to fall away and the 

 drogue to deploy. The entire process normally 

 takes only a few minutes. 



1979 OPERATIONS 



During the 1979 season 5 BTT's were deployed 

 in support of IIP operations (Table 1). Three 

 BTT's, 2605, 2600 and 2604, were deployed in the 

 Labrador Current, BTT 2601 was deployed to the 

 east of the Labrador Current and BTT 2602 was 

 deployed northeast of Flemish Cap. All 5 BTT's 

 functioned well throughout the season. A total 

 downtime of 18 days (7.7% of the season) was 

 experienced on the LUT due largely to its 

 developmental nature. Accuracy of positions was 

 not as good as the 3 km normally attainable 

 because of inadequacy of reference platforms. 

 However, comparison of BTT positions with 

 reported deployment positions and known 

 locations of relatively swift moving currents such 

 as the Labrador Current indicated positions were 

 within ±10 km. Exact errors could not be 

 determined. 



B-2 



