Human gravity-gradient noise in interferometric gravitational-wave detectors - art. no. 082001.

Among all forms of routine human activity, the one which produces the stron gest gravity-gradient noise in interferometric gravitational-wave detectors (e.g. LIGO) is the beginning and end of weight transfer from one foot to t he other during walking. The beginning and end of weight transfer entail sh arp changes (time scale tau similar to 20 msec) in the horizontal jerk (fir st time derivative of acceleration) of a person's center of mass. These jer k pairs, occurring about twice per second, will produce gravity-gradient no ise in LIGO in the frequency band 2.5 Hz less than or similar to f less tha n or similar to 1/(2 tau) similar or equal to 25 Hz with the form root S-h( f) similar to 0.6 x 10(-23) Hz(-1/2) (f/10 Hz)(-6)[Sigma(i)(r(i)/10 m)(-6)] (1/2) Here the sum is over all the walking people, r(i) is the distance of the i'th person from the nearest interferometer test mass, and we estimate this formula to be accurate to within a factor 3. To ensure that this noise is negligible in advanced LIGO interferometers, people should be prevented from coming nearer to the test masses than r similar or equal to 10 m. A r similar or equal to 10 m exclusion zone will also reduce to an acceptable level gravity gradient noise from the slamming of a door and the striking o f a fist against a wall. The dominant gravity-gradient noise from automobil es and other vehicles is probably that from decelerating to rest. To keep t his below the sensitivity of advanced LIGO interferometers will require kee ping vehicles at least 30 m from all test masses. [S0556-2821(99)03418-9].