Terminology

B4 Data Description

Terminology:

A Fault Segment is any line or an area of faulting which had been identified by the survey team as being of interest for the B4 ALSM project. Of the San Andreas Fault system, the B4 project focused on surveying the main strand of the San Andreas from Bombay Beach to Parkfield. In addition to this main strand we mapped the Banning and the Mission Creek segments of the San Andreas Fault. Along the San Jacinto Fault system we surveyed from the Superstition Mountains near El Centro to Cajon Pass near Wrightwood. We included the Coyote Creek fault, the Clark fault, and the Buck Ridge fault on the San Jacinto.

A Survey Segment is a line or an area of an identified Fault Segment which is almost always surveyed as a single unit. This is an organizational scheme implemented for coordinating efforts between GPS surveyors on the ground and the operators of the laser in the airplane. Though it was initially intended only for the organization of the project, the Survey Segments are the organizational scheme for ALL DATA produced by the B4 project. The ALSM data for one Survey Segment isn’t necessarily collected in one session of surveying. SAF11 is an example of a Survey Segment which was flown all in one Flight, whereas SAF10 was flown in two separate Flights.

Coupled Survey Segments are two or more Survey Segments which will employ essentially identical sets of GPS control data, and so as the laser equipped airplane moves from one part of a Coupled Segment to the next, the ground crews are not required to move. The only occurrence of this during the B4 survey was at SJF01 where the two strands of the San Jacinto near the Superstition Mountains were defined as one segment and therefore surveyed in one Flight.

A Flight is a period of time defined by the take-off and landing of the laser equipped airplane. Every flight in the B4 survey had one on/off session for the complete Optech system (this is not to be confused with the laser itself which can be turned on and off while the rest of the Optech system is running). A Survey Segment may be surveyed with a number of different Flights (e.g. SAF10 was surveyed by Flights 138A and 138B and SAF06 was surveyed by Flights 139B and 140A). And one Flight may collect ALSM data for several different Survey Segments (Flight 143A collected data for Survey Segments SAF01, SJF02 and SJF03). One of the defining characteristics of a Flight is that the complete Optech system should remain on throughout the Flight. Each flight of the B4 survey has a corresponding raw file, a .range file. This is in Optech’s proprietary format and is encoded so that only users of the REALM software can process it.

A Sub Pass is defined as the area over which ALSM data was collected during one on/off period of the laser. Passes are organized by Survey Segment, Flight, and on/off time. Each Sub Pass collects data in an ~400 meter swath along the flight’s trajectory. There were occasions when a failure in the laser or a sharp angle in the Fault Segment prevented the laser from running uninterrupted from one end of the Survey Segment to another. At this time there is no way of obtaining a DEM of a solitary Sub Pass.

A Complete Pass is a Sub Pass or a composite of two or more Sub Passes which completes one of the five lines of ALSM data that in turn completes the ALSM data coverage for a Survey Segment (BAN02 contains more than five Complete Passes). For each Fault Segment identified for surveying we planned to have a dense coverage with five Complete Passes running parallel to the Fault Segment, each Pass having a ~400 meter swath. These five Complete Passes make up our goal of a 1km swath (lots of overlap).

A Calibration Pass is a pass which is perpendicular to the Complete Passes for a segment and is used to calibrate the ALSM data. It is usually flown at the same altitude as the Complete Passes and it usually has the same swath as the Complete Passes.

The Passes have been organized according to time and according to geometry. The naming scheme for the Passes is as follows. Each Complete Pass is numbered from Southwest to Northeast. Each Sub Pass of a Complete Pass is assigned a letter A, B, C, etc. from Southeast to Northwest. In the case of SAF11 all the Sub Passes are Complete Passes

red line is Sub Pass SAF11_138a_1A
dark orange line is Sub Pass SAF11_138a_2A
light orange line is Sub Pass SAF11_138a_3A
yellow line is Sub Pass SAF11_138a_4A
light green line is Sub Pass SAF11_138a_5A

And for SAF08, which is more complicated, the Sub Passes would be as follows:

dark orange line is Sub Pass SAF08_139a_1A
red line is Sub Pass SAF08_139a_1B
purple line is Sub Pass SAF08_139b_1C
light orange line is Sub Pass SAF08_139a_2A
turquoise line is Sub Pass SAF08_138b_2B
yellow line is Sub Pass SAF08_139a_3A
blue line is Sub Pass SAF08_139b_3B
light green line is Sub Pass SAF08_139a_4A
dark blue line is Sub Pass SAF08_139b_4B
dark green line is Sub Pass SAF08_139a_5A
light purple line is Sub Pass SAF08_139b_5B

For every Pass made during the survey there is a corresponding .all file which is output by Optech’s processing software REALM. At this time no DEMs have been created using only one Sub Pass, but the opportunity is available to someone who has access to software like Terrascan. All of the .all files are archived at OSU.

Email questions or comments to kendrick.42@osu.edu