Ground control point locations for the UAS survey of the Los Padres Reservoir delta, Carmel River valley, CA, 2017-11-01

Ground control was established using ground control points (GCPs) consisting of small square tarps with black-and-white cross patterns placed on the ground surface throughout the survey area. The GCP positions were measured using survey-grade GPS receivers operating in real-time kinematic (RTK) mode. For each GCP measurement the GPS receiver was placed on a fixed-height tripod and set to occupy each GCP for a minimum occupation time of one minute. The RTK corrections were referenced to a GPS base station occupying a previously established benchmark designated SFML, located on the Los Padres Reservoir dam approximately 1 kilometer from the survey area. In order to ensure consistency with historic surveys, the previously established position for SFML published in Smith and others, 2009 was used for the real-time surveys. After the survey, the static occupation on SFML was submitted to the National Geodetic Survey (NGS) Online Positioning User Service (OPUS).

A uniform adjustment was applied to the GCPs to shift the positions from the historic reference frame published in Smith and others, 2009 to the updated reference frame observed at the SFML benchmark during the 2017 survey (derived using the National Geodetic Survey (NGS) Online Positioning User Service (OPUS)).
To ensure consistency with historic data sets, the original published position for the SFML benchmark was used for the RTK GPS base station position. Thus, the GCP positions and original SfM data products were consistent with the historic data presented in Smith and others, 2009. The SFML benchmark position published in that report is (in UTM zone 10 coordinates relative to the NAD83 reference frame): Northing: 4027605.397 Easting: 619388.986 Ortho. Ht. [m, NAVD88]: 322.418 (GEOID03)
After the 2017-11-01 UAS survey, the 5:40 static GPS occupation on SFML was submitted to NGS OPS which derived the following current-epoch position for SFML: Northing: 4027605.687 Easting: 619388.761 Ortho. Ht. [m, NAVD88]: 322.359 (using GEOID03 separation = -33.047 m)
Thus, the displacement between the 2009 published SFML position and the 2017-11-01 observed position is: dN: +0.290 meters dE: -0.225 meters dElev.: -0.059 meters
This magnitude and direction of displacement is similar to those estimated for this location by the National Geodetic Survey Horizontal Time-Dependent Positioning (HTDP), shown below: HTDP OUTPUT, VERSION 3.4.0 DISPLACEMENTS IN METERS RELATIVE TO NAD_83(2011/CORS96/2007) FROM 11-05-2008 TO 11-01-2017 (month-day-year) FROM 2008.847 TO 2017.835 (decimal years) NAME OF SITE: SFML LATITUDE: 36 23 10.23945 N LONGITUDE: 121 40 7.85831 W NORTH: 0.341 meters EAST: -0.241 meters UP: -0.012 meters
To produce the final data products for this data release, all data were transformed from the historic reference frame into the current-epoch reference frame consistent with the 2017-11-01 observed position for SFML. This transformation was done using a uniform horizontal and vertical adjustment applied to each data set.
For adjustment of the GCPs, the horizontal and vertical displacements were applied to the northing, easting, and elevation coordinates to shift them into the updated reference frame.