1. Towards Optimizing the determination of accurate heights with GNSS OCTOBER 9, 2014 Dan Gillins, Ph.D., P.L.S.

2. Current Research Efforts 1.Optimizing the determination of accurate heights with GNSS (NGS) NGS 58/59 guidelines OPUS-RS, OPUS-S, OPUS Projects GPS+GLONASS vs. GPS-only Real-time networks 2.UAV remote sensing Evaluating accuracy of current practice Improving data collection and processing steps 3.Earthquake hazard mapping Megaquake-induced liquefaction (USGS) Liquefaction & lateral spreading hazard maps (USGS) O-HELP: a web-based GIS tool for assessing earthquake hazards in Oregon (CLiP) 4.GNSS surveying in forested environments

3. Importance of Research Accurate heights are crucial for a multitude of scientific studies and engineering projects monitoring deformations, engineering layout, flood mapping, sea level rise, development of nautical charts, topographic mapping, crustal movement, subsidence studies Geodetic leveling remains the most accurate form of obtaining heights Requires line-of-sight, slow (expensive), prone to errors GPS has revolutionized the surveying of geodetic networks Does not require line-of-sight, easy to use, quite accurate It is desirable to take advantage of the economics of GPS to determine ellipsoidal and orthometric heights January 14, 2016 2

4. Testing and Improving NGS 58/59 Height Modernization Guidelines Objectives: Evaluate NOS NGS 58 and 59 guidelines Follow guidelines to establish a control network from Salem to Corvallis 20 varying benchmarks B versus C stability under varying canopies Recommend new guidance based on current technology Use of GLONASS? Improved hybrid geiod models (GEOID12A, GEOID14) Use of modern GNSS antennas+receivers Improved accuracy and availability of GNSS orbits Real-time networks Various processing tools OPUS, OPUS Projects Star*Net January 14, 2016 3

5. Summer 2014 Height Mod. Survey January 14, 2016 4 Collect static GPS+GLONASS data 10 total days of surveying 3 days of 5 hour sessions (primary network), 7 days of 1 hour sessions (secondary network) 5 receivers (6 for 3 days) 20 marks covering 350 square miles 28 total unique sessions 264 total baselines observed 103 independent baselines obtained after removing outliers (avg. length 10.79 km)

6. January 14, 2016 5 Phase 2: Static Survey

7. Phase 3: Find ellipsoidal heights following NGS 58 Use only GPS data Partially constrained the HARN stations according to their reported NGS network accuracies Average 95% confidence on ellipsoidal height =1.23 cm Only 1 mark exceeded 2 cm from the published NGS ellipsoidal height (N99RESET) J54 appears to have been disturbed January 14, 2016 6 StationdNdEdZ 95% Confidence Ellipsoidal height (cm) U7270.0035-0.00090.0081*0.8403 G728-0.0031-0.0028-0.0005*0.9270 NESMITH-0.00050.0016-0.0053*0.9270 BICKFORD-0.0052-0.0028-0.0096*1.0664 S714-0.00740.00050.0158*0.9270 N99RESET0.00360.0058-0.0229*0.9746 J990.0034-0.0117-0.0118*1.3146 Y6830.0061-0.0073-0.0032*1.1725 BEEF-0.0021-0.00170.0173*1.1571 PRICE0.02070.0144-0.0009*1.3712 G2870.00360.00370.0038*1.3323 J54-0.0487-0.0617-0.0114*1.6302 T7140.0037-0.003-0.0028*1.3932 CORVA0.0037-0.0073-0.0033*1.4946 D728 1.4782 MAG 1.2049 PEAVN/A 1.3193 Z714 1.2652 Q388RESETN/A 1.3712 PEAKN/A 1.4577

8. Next Steps 1.Determine which benchmarks have "valid" orthometric heights 2.Identify any needs to conduct geodetic leveling as a redundancy check 3.Repeat study using other techniques 1.GPS+GLONASS (compare with GPS-only results) 2.Rapid ephemerides instead of precise ephemerides 3.Use of OPUS-S, OPUS-RS, and OPUS Projects 4.Use of Oregon Real Time Network (ORGN) 1.Single base versus real-time networks 2.GPS only versus GLONASS 5.Use of Star*NET versus ADJUST versus OPUS-Projects 4.Give recommendations for optimizing the determination of accurate heights January 14, 2016 7