The Skyquake Bench: The Cone and the Array

THE SKYQUAKE BENCH · D148 p. 31 × CATES AND STURTEVANT 2002
A Mach cone over 205 seismic stations: what the array records, and the sentence the record built on it
the cone's half-angle is arcsin(1/M); each ray refracts through the ISA and lands, or turns back
below the ground's sound speed no direct boom arrives: the cutoff Mach, the paper's eq. 5
the stations, the ISA, the trace and the fit are exact; the vehicle, its staging and Carlson's factors are dials
the record reports the 1991 and 1992 booms traced to two F-4s; the paper it cites reads them as indirect booms from offshore
fly the cone · read the array · hear the ground · find the cutoff · open the file

Evidence

fact ⇄ what kind of claim · live

D148 p. 31: 200 stations at 1 to 20 Hz; the SR-71 at Mach 3.2 on 9 December 1993; STS-42 on 30 January 1992; another Discovery pass read as Mach 14 at 55 km from 66 stations over 500 km; the 1991 and 1992 booms 'traced to two F-4 Phantom aircraft … at speeds near Mach 1'

the record's statements, with Cates and Sturtevant 2002 as its footnote

REPORTED

The paper: over 200 stations at 100 samples a second; 1.5 to 2 µm/s per Pa; the SR-71 at Mach 3.15 and 21 km; the seven Thursdays; the U.S.G.S., Lincoln Labs and its own reads; 'indirect booms from a source offshore'

the paper's own statements and findings; nothing added from outside it

REPORTED

205 CI stations operating on 9 December 1993, with their places and heights; the coastline and borders

the FDSN station service at Caltech; Natural Earth (today's lines)

DOCUMENTED

The ISA, the Mach angle, the ray trace and its cutoff, the arrival times, the still-air hyperbola and its fit

arithmetic on the standard atmosphere, the paper's eq. 5 and the still-air cone; no constant fitted to the record

EXACT

The vehicle and its staging, no wind, the ground's ΔT, Carlson's overpressure with K_p = K_t = 1, the shape factor and length, the coupling, the trace shape

choices, shown as dials; every figure is quoted with them

MODELLED

Whether the array found two F-4s, as the record says, or indirect booms from offshore, as the paper the record cites says

the question this bench leaves to you

READING