11. Beginning the Survey

We have arrived at the beginning of the survey. The survey plan is to have the ship steam back and forth in a series of straight lines between the Golden Gate bridge on the west and the region just to the east of Alcatraz Island (alternating the direction of the ship moving first from east to west and then from west to east, back and forth), as the multibeam sonar system produces a map of the seafloor below. We will start at the southeast portion of the survey region and as we collect line after line of data, we will slowly work our way north. Remember the entire survey will take 9 days.

Image source USGS

With each passage of the ship, the multibeam sonar system will produce an image of a swath of bay floor (see image below). The swaths along adjacent ship tracks will overlap, so there will be a redundancy in the data, which will be used to check for errors and any malfunctions of the multibeam and GPS navigation systems.

Main Menu Expedition Menu 1. Welcome 2. The Idea 3. Boarding 4. Ship Tour 5. Back Deck 6. Preparing to Depart 7. Leaving 8. Meeting 9. Bay-Delta-Estuary 10. Navigating 11. The Survey 12. First Data 13. The Mosaic 14. Visualizing 15. Hazards 16. Disposal Site 17. Sediment Map 18. Compare 19. Future Studies 20. Final Meeting Contact Don Reed Dept. of Geology San José State University	We have arrived at the beginning of the survey. The survey plan is to have the ship steam back and forth in a series of straight lines between the Golden Gate bridge on the west and the region just to the east of Alcatraz Island (alternating the direction of the ship moving first from east to west and then from west to east, back and forth), as the multibeam sonar system produces a map of the seafloor below. We will start at the southeast portion of the survey region and as we collect line after line of data, we will slowly work our way north. Remember the entire survey will take 9 days. Image source USGS With each passage of the ship, the multibeam sonar system will produce an image of a swath of bay floor (see image below). The swaths along adjacent ship tracks will overlap, so there will be a redundancy in the data, which will be used to check for errors and any malfunctions of the multibeam and GPS navigation systems.
	The bathymetry (water depth) data are determined from the traveltime of the sonar signals – how long it takes for the signal to go from the multibeam transducer array mounted near the water line on the bow of our ship, down to the seafloor and back to the back of the ship. Remember that for every signal that is sent out from the transducer array, many signals are returned, each from a different location along the swath oriented perpendicular to the vessel. Through the beauty of multibeam and GPS navigation, we can keep track of the locations where the sonar signal bounces off the bay floor and by measuring the traveltime, we can detemine the distance to the ship and therefore, the water depth.	Image source USGS
	In addition to the measurement of the water depth, we can use the strength of the sonar return (echo), we can make inferences about the "roughness" of the bay floor.
	Let’s collect our first swath of seafloor data

Expedition Menu

1. Welcome 2. The Idea 3. Boarding 4. Ship Tour 5. Back Deck 6. Preparing to Depart 7. Leaving 8. Meeting 9. Bay-Delta-Estuary 10. Navigating 11. The Survey 12. First Data 13. The Mosaic 14. Visualizing 15. Hazards 16. Disposal Site 17. Sediment Map 18. Compare

19. Future Studies

20. Final Meeting

Contact Don Reed Dept. of Geology San José State University

1. Welcome

2. The Idea

3. Boarding

4. Ship Tour

5. Back Deck

6. Preparing to Depart

7. Leaving

8. Meeting

9. Bay-Delta-Estuary

10. Navigating

11. The Survey

12. First Data

13. The Mosaic

14. Visualizing

15. Hazards

16. Disposal Site

17. Sediment Map

18. Compare

Contact
Don Reed
Dept. of Geology
San José State
University