# Ligo detector signal calibration **URL:** \ **Category:** Data Analysis\ **Created:** [July 8, 2024, 11:52pm UTC](https://ask.igwn.org/t/ligo-detector-signal-calibration/1071 "2024-07-08T23:52:22Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![mjy](https://avatars.discourse-cdn.com/v4/letter/m/ecccb3/32.png) [@mjy](https://ask.igwn.org/u/mjy)\ **Post date:** [July 8, 2024, 11:52pm UTC](https://ask.igwn.org/t/ligo-detector-signal-calibration/1071/1 "2024-07-08T23:52:22Z")
What is the cause for large relative signal strength fluctuations between L1 and H1, of +/- 20%? ---
**Author:** ![mjy](https://avatars.discourse-cdn.com/v4/letter/m/ecccb3/32.png) [@mjy](https://ask.igwn.org/u/mjy)\ **Post date:** [July 25, 2024, 4:54pm UTC](https://ask.igwn.org/t/ligo-detector-signal-calibration/1071/3 "2024-07-25T16:54:34Z")
Just to be more specific, here is a plot that shows relative timing and signal strength ratio for most of the published GW events. (reposted to correct a mistake) ![event_results](https://canada1.discourse-cdn.com/flex031/uploads/gwosc/original/1X/3c08c8e4e0dc2491bdd3fa095f0a33caee3fa474.png) ---
**Author:** ![jonah](https://yyz1.discourse-cdn.com/flex031/user_avatar/ask.igwn.org/jonah/32/10_2.png) [@jonah](https://ask.igwn.org/u/jonah)\ **Post date:** [July 30, 2024, 11:35pm UTC](https://ask.igwn.org/t/ligo-detector-signal-calibration/1071/4 "2024-07-30T23:35:00Z")
Hi! I’m sorry, I’m not exactly sure what you mean by “signal ratio”. Do you mean a ratio of SNR’s? Or peak strain amplitude? Or something different? In any case, the amplitude of a signal as measured in H1 and L1 will not necessarily match exactly, as there are differences in the antenna response of each detector, which depends on the sky position and orientation of the source. Similarly, the time difference between the two instruments depends on the sky position of the source. If you are looking at SNR ratios, there is also a difference due to the relative sensitivity of each instrument. There are lots of places to read about this, but it looks like Drew Keppel has an introduction to antenna patterns in his dissertation. Good luck! [https://thesis.library.caltech.edu/1901/](https://thesis.library.caltech.edu/1901/) ---
**Author:** ![mjy](https://avatars.discourse-cdn.com/v4/letter/m/ecccb3/32.png) [@mjy](https://ask.igwn.org/u/mjy)\ **Post date:** [August 6, 2024, 8:07pm UTC](https://ask.igwn.org/t/ligo-detector-signal-calibration/1071/5 "2024-08-06T20:07:49Z")
Hi, thanks for replying. Is antenna response same as interferometer response? Your answer is what I was looking for, and specifically the equations 3.20a & 3.20b in D. Keppel’s dissertation. However, I was not able to reproduce the display shown in page 34, for cross Fx, unless I square cosθ in the second part of eq. 3.20b, cosθsin2φcos2ψ. It would be interesting to know which is correct. Given that antenna response depends on sky location of signal source, where can we find the information on the orientation of L1 and H1, with respect to each other or with some reference. ---
**Author:** ![jonah](https://yyz1.discourse-cdn.com/flex031/user_avatar/ask.igwn.org/jonah/32/10_2.png) [@jonah](https://ask.igwn.org/u/jonah)\ **Post date:** [August 7, 2024, 4:32pm UTC](https://ask.igwn.org/t/ligo-detector-signal-calibration/1071/6 "2024-08-07T16:32:14Z")
@mjy The pyCBC package includes methods for printing out the detector locations: [https://pycbc.org/pycbc/latest/html/detector.html](https://pycbc.org/pycbc/latest/html/detector.html) The same package can also be used to compute the antenna response for a particular sky position and orientation. If you’d like to see how these are computed, one option is to look at the source code. Also, there are lots of papers and text books that cover this topic. Another option is this paper by Bernard Schutz, “Networks of gravitational wave detectors and three figures of merit”. I think it covers antenna factors pretty well: > **[Networks of gravitational wave detectors and three figures of merit](https://arxiv.org/abs/1102.5421)** > > This paper develops a general framework for studying the effectiveness of networks of interferometric gravitational wave detectors and then uses it to show that enlarging the existing LIGO-VIRGO network with one or more planned or proposed detectors... ---
**Author:** ![mjy](https://avatars.discourse-cdn.com/v4/letter/m/ecccb3/32.png) [@mjy](https://ask.igwn.org/u/mjy)\ **Post date:** [August 9, 2024, 4:15am UTC](https://ask.igwn.org/t/ligo-detector-signal-calibration/1071/7 "2024-08-09T04:15:31Z")
Thanks for your reference. Will take a look.