Glossary of Terms
Glossary Note: Comments, corrections, or suggestions for new glossary terms can be submitted via our TLA Request Form.
adiabatic approximation: (a) waveform generation; the approximation method of building an insprialing trajectory and associated gravitational waveforms through a succession of geodesic orbits; (b) detector response; in the adiabatic approximation the LISA response at any moment of time is calculated assuming that the LISA sciencecraft are fixed in space: i.e., that they are not moving in the solar system barycenter frame.
constellation: The three LISA spacecraft, including their relative positions and orientations, viewed as a unit.
data processing: The act of producing a LISA Data Product, suitable for science analysis (see below), from phase or other measurements made at the LISA sciencecraft.
ephemeris: A table giving the position and oriention of the LISA constellation as regular intervals throughout the observation period.
first generation TDI: time-delay interferometery (see TDI below) variables that cancel laser frequency noise in the approximation that LISA constellation arm lengths are constant in time.
TDI: (acronym) time-delay interferometery
guiding center: The unique location in the constellation plane that is equidistant from each of the three LISA sciencecraft. It is the "location'' of LISA for the purpose of the ephemeris and the origin of the LISA Detector Frame (see LDF below).
HDF5: (acronym) Hierarchical Data Format (version 5). The SLDP is implemented on top of HDF5.
LISA Simulator: A particular program that simulates the LISA response to incident gravitational waves. The LISA Simulator neglects the order O(hv) corrections to the response, owing to the velocity v of the sciencecraft and the gravitational strain perturbation h measured in the solar system barycentre frame, and approximates the LISA sciencecraft orbital ephemeris by working only to second order in orbital eccentricy and neglecting planetary and other solar system perturbations. See also Synthetic LISA.
low-frequency limit/approximation: The low-frequency limit (also referred to as the small-antenna limit or long-wavelength limit) is an approximation to the the LISA response that keeps only terms of lowest order in fL, where f is the gravitational wave frequency and L is the separation between LISA sciencecraft.
Michelson variables: The Michelson variables described are the difference, at each vertex, in the light phase of the light returning to the vertex from each of the other two sciencecraft: i.e., they describe the output of a Michelson interferometer synthesized from the phase measurements made at each vertex. Owing to the significantly mis-matched armlengths in the LISA constellation, laser frequency contributes strongly to the noise in the Michelson variables.
observable(s): A function of the phase measurements made at one or more LISA sciencecraft, which are used for the analysis of LISA data.
response scalar/response function: In the small antenna limit the response of the LISA constellation to incident gravitational waves can be described in terms of geometric factors and a single function of time associated with each vertex science craft. At frequencies where the small antenna limit is no longer valid the response function becomes a function of gravitational wave frequency as well.
rigid adiabatic approximation: the combination of the rigid and the adiabatic approximations as they apply to the detector response.
rigid approximation: In the rigid approximation the LISA sciencecraft move as a rigid body: i.e., the separations and vetex angles are constant in time.
sciencecraft: One spacecraft bus with its LISA Scientific Complement.
science analysis: Detailed examination of a LISA Data Product for the purpose of understanding the physics or astrophysics of gravitational waves, astrophysical or astronomical phenomena.
second generation TDI: Time domain interferometery variables constructed to cancel laser frequency noise for moving LISA spacecraft (contrast with first generation TDI above).
small-antenna limit/approximation: See long-wavelength limit/approximation above.
SLDP: (acronym) Simulated LISA Data Product. The principal enabling technology of the TLA Project.
Synthetic LISA: A program that generates time series of the LISA fundamental noises, as filtered through a wide range of first and second order TDI observables. Synthetic LISA can also compute the TDI responses to gravitational waves. Synthetic LISA neglects the order O(hv) corrections to the response, owing to the velocity v of the sciencecraft and the gravitational strain perturbation h measured in the solar system barycentre frame, and approximates the LISA sciencecraft orbital ephemeris by working only to second order in orbital eccentricy and neglecting planetary and other solar system perturbations. See also LISA Simulator.
TLA: (acronym) Testbed for LISA Analysis
