Hanford Observatory

Mentor: Fred Raab
SURF-99 Student: Eric Morganson, California Institute of Technology, Pasadena, CA
SST Research Sites: LIGO Hanford Observatory and Gladstone High School, Gladstone, OR
SST Research Team Leader: Mr. Dale Ingram, Gladstone High School
SST Research Team Students: Andrew Gaynor, Erin Hewett and David Wells, Gladstone High School

SURF-99 Project Description:

One of the unique features of LIGO interferometers is that they are susceptible to earth tides. Changing gravitational forces from the sun and moon produce deformations of earth's crust underneath the interferometers. This crustal distortion will move the observatory end stations by a large fraction of a millimeter relative to the corner station. The LIGO design incorporates actuators in the laser and seismic isolation systems to continuously remove these tidal effects. Actuator ranges were determined based on estimates of maximum tidal distortion (see earth_tides.pdf). As LIGO interferometers turn on, it will be interesting to compare an idealized model of tidal distortions to measured tidal compensation signals. If sufficiently good agreement can be obtained it may become possible to achieve feedforward compensation of the tides and it will certainly become easier to identify other long term drifts in the interferometer. This project will entail using the literature to develop an idealized tidal model for a homogeneous earth. Once this is working, additional terms with adjustable strength parameters can be added to account for inhomogeneities due to local geological features, effects of ocean loading, temperature and insolation cycles, etc.

Significant experience with statistical analysis and least-squares adjustment of parameters will be gained during this project. The product will be C programs and associated documentation for analyzing tidal deformations and other corrections to the lengths of LIGO's arms. Unfortunately, tidal data may not become available for comparison during summer 99. However a collaborating team from Gladstone High School, that has a multiyear research commitment, will analyze tidal data using this model as soon as it becomes available. This data will be shared among all participants in this research effort.

Outline for Earth-Tide Modeling:

*  Develop Analysis Methods and C Programs for Earth Tides and Related Effects
                      (in collaboration with Gladstone SST Research Team)
-Ideal earth-tide calculation
-Parametrized earth-tide model (ETM) using calculation as basis
-Ocean-loading enhancement to ETM
-Tilt enhancement to ETM
-Temperature enhancement to ETM
-Insolation enhancement to ETM

The Gladstone SST team (see photo at left) will develop a multiyear research program that will be based at LIGO Hanford Observatory (LHO) during summers and will be based at Gladstone High School (GHS) during the academic year. Using modern internet and teleconferencing tools the team will acquire data at LHO and perform computing-resource-intensive pre-processing of data on LHO computing equipment; this pre-processed data will then be downloaded to a GHS computer for further human-resource-intensive data analysis. The Gladstone team will analyze low frequency motions of the LIGO buildings that affect the lengths of LIGO's arms. These include fundamental earth motions, like earth tides (see earth_tides.pdf) and the microseism (see museism.pdf), and modifications due to local topography. Research products that are deliverables of the GHS team are listed in the outline below.

Summer residency at LHO will provide the GHS team members ready access to world-class scientific expertise and equipment; academic-year activities at GHS will be the seed of a research-based course offering. On Fridays during the summer, the GHS team members will participate with colleagues from more than a dozen other high schools and with educational professionals in SST workshops run by our partners at Pacific Northwest National Laboratory (PNNL). These workshops (see SST_Friday_menu.pdf) will aid the SST teams to develop realistic plans and techniques to integrate their research programs back at the high school.  Regular teleconferences during the academic year between the GHS team members and LHO scientists and engineers will ensure timely progress toward project research goals.

Analysis & Feedforward Compensation of Low-Frequency Seismicity

*  Analyze Data on Earth Tides and Related Effects
                       (in collaboration with Eric Morgonson)
 -Comparisons to ideal earth-tide model
 -Evaluation of ocean-loading enhancement to ETM
 -Evaluation of tilt enhancement to ETM
 -Evaluation of temperature enhancement to ETM
 -Evaluation of insolation enhancement to ETM
 
*  Microseism Characterizaion
 -Survey: Is microseism uniform across technical foundation?
 -Identify sources of information on ocean wave activity
  > Coast Guard?
  > NOAA buoys?
  > Satellite data?
 -Evaluate correlation w/ ocean data
 -Characterize microseism in tilt, vertical, horizontal DOFs
 -Evaluate correlations between buildings on site
 
*  Microseism (museism) Subtraction
 -Use corner/end station seismometers to fit out mid-station museism
            (This prior to availability of interferometer arm signals)
 -Use seismometer signals to fit out interferometer museism signals

*  Use Seismometers for Microseismic Feedforward Signals to Seismic Actuators
 -Develop C++ Modules w/ LIGO CDS guidance
 -Experimentally evaluate performance
 -Work with LIGO CDS to engineer final product

Last modified June 14, 1999.
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