Projected baseline, delay and complex visibility
Research context
research method · conditional · As of 2026-10-10
A far-field source produces a geometric delay b·s/c between two antennas.
Key knowledge
A far-field source produces a geometric delay b·s/c between two antennas. Correlated electric fields define complex visibility; the phase sign depends on antenna order and the chosen Fourier convention. Baseline length alone does not specify the projected angular information.
Values and equations
τ_g=b·s/c; Δφ=2π b·s/λ; V(u,v)=integral A(l,m) Iν(l,m) exp[-2πi(ul+vm)] dl dm
- b
- Ordered baseline vector m
- s
- Source direction unit vector 1
- τ_g
- Geometric delay s
- λ
- Wavelength m
- u,v
- Projected baseline components divided by λ 1
- l,m
- Small-field direction cosines 1
- A
- Primary-beam response 1
- Iν
- Angular specific intensity W m^-2 Hz^-1 sr^-1
- V
- Flux-density visibility under this angular convention W m^-2 Hz^-1
Conditions and scope
- Incoherent sky, narrowband observation and far-field approximation; remove phase-centre delay before imaging.
- Visibility amplitude needs a declared flux normalization and calibrated antenna response.
- Flat small-field approximation; normalized visibility is V(u,v)/V(0,0) when V(0,0) is nonzero.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Introduction to radio interferometry: Slides 5–22: geometric delay, complex visibility, Fourier sampling and imaging (selected source body inspected).
2026-10-10 · Bounded source check of the recorded statement and conditions. This does not certify a unique physical model, reproduce the cited study or replace independent branch review.
Entry details
Permanent link to this entry ↗- Record identity
- research-earth-radio-delay
- Revision
- research.1
- Structured reference record
- Postgraduate & research reference