Spray Activities for ASAP. Scripps Institution of Oceanography Russ Davis Jeff Sherman Jim Dufour Brent Jones 1. Array design and glider routing 2. Field operations and new technical developments 3. Science - define scales – map measured velocity
Spray Activities for ASAP
Scripps Institution of Oceanography
1. Array design and glider routing
2. Field operations and new technical developments
3. Science - define scales – map measured velocity
the role of surface layer and eddies in upwelling
evaluate glider control strategies
1. A derivative from Snell’s Law provides most rapid path through known steady current between points A and B
General rule: In an adverse or perpendicular currents, go directly across the current. In weak or favorable currents head toward target.
2. A simple modified “current bucking” algorithm keeps gliders near prescribed track
General rule: Staying close to the track slows progress and can destroy mapping skill
3. Direct optimization of an array’s mapping skill leads to complex patterns of data distribution not suitable for human analysis
4. Direct optimization of mapping skill along “ideal tracks” provides a usable basis for automatic steering and inter-vehicle coordination
Minimum travel time is found is found from first variation as Snell’s Law derives from Fermat’s Principle.
Dark lines are fastest paths from y=0 through current shown in red.
Light lines are second fastest extremum of travel time. This is analogous to the multiple “rays” found from Snell’s Law.
Head toward “steering point” (red diamond) using current compensation. Used during much of MB2006.Works poorly when vehicle is far from track.
As each glider surfaces, it is given the heading that maximizes mapping skill upon arrival.
Avoids vehicle bunching on field correlation scale.
Tuning with an attractor to the track keeps gliders near their ideal paths as they approach/pass each other.
Yields only a local optimum.
1. One Spray constructed. Four prepared with CTD (pumped), Chlorophyll-a fluorometer, and 750 kHz ADCP ( ~ 25 m range)
2. Four units deployed near Moss Landing July 18-20 and recovered September 2 without interruption.
3. All sensors performed nominally. Measured 4527 profiles of T, S, fluorescence, acoustic backscatter and directly-measured velocity.
4. Optics and CTD that use pumped system were unaffected by biofouling that reduced the speed of one unit to a dangerous level
5. Sprays focused sampling on perimeter of control volume where ADCP add significantly to flux measurements
6. Limitations to controlling sampling were not strategy but inability to overcome 25 cm/s vertically averaged currents
Figure shows array perimeter and typical station spacing. Sections between red marks were patrolled by oscillating “rocker” Spray
1. Find objective-mapping skill if vehicles move in perfect synchronism.
2. Compare with actual skill
Skill vs. perimeter distance at various times in a cycle of four perfectly synchronized vehicles advancing at 25 cm/s
3. Array at peak behavior
2. Array begins to recover
1. Strong poleward current thwarts coordination
4. Allocation to interior ideal paths to replace Slocums degrades array performance