<p><strong>It depends.</strong></p>

<p>Caveat: my experience is with reflection seismic surveys, but I think many of the principles are similar to MASW.</p>

<p>As you guessed: it's an optimization problem. There are lots of factors at play. It's up to the geophysicist to balance the various needs of the survey:</p>

<ul>
<li>You need to image the target with useful accuracy (small natural bin size).</li>
<li>You want useful signal:noise levels (high fold and trace density).</li>
<li>You want near offsets for good estimates of P-wave reflectivity.</li>
<li>You want far offsets for good estimates of elastic properties (e.g. density).</li>
<li>You may need far offsets to image certain types of geology.</li>
<li>You want the acquisition crew to have enough receivers for the design.</li>
<li>You want to be able to afford the acquisition and processing!</li>
</ul>

<p>A while ago, I wrote a blog post on the subject: <em><a href="http://www.agilegeoscience.com/blog/2012/9/6/fold-for-sale.html" rel="nofollow noreferrer">Fold for sale</a></em>. It's about balancing fold (how many traces go into the stack, basically, a big driver of signal:noise) with cost.</p>

<p>My colleague Evan Bianco and I also did a series on modelling seismic acquisition. If you're into Python at all, there's some code to play with:</p>

<ul>
<li><em><a href="http://www.agilegeoscience.com/blog/2014/12/11/the-race-for-useful-offsets.html" rel="nofollow noreferrer">The race for useful offsets</a></em></li>
<li><em><a href="http://www.agilegeoscience.com/blog/2014/12/17/laying-out-a-seismic-survey.html" rel="nofollow noreferrer">Laying out a seismic survey</a></em></li>
<li><em><a href="http://www.agilegeoscience.com/blog/2015/1/8/it-goes-in-the-bin" rel="nofollow noreferrer">It goes in the bin</a></em></li>
<li><em><a href="http://www.agilegeoscience.com/blog/2015/1/14/seismic-survey-layout-from-theory-to-practice" rel="nofollow noreferrer">Seismic survey layout: from theory to practice</a></em></li>
</ul>

<p>The greatest minimum offset in a bin is an important consideration, as you guessed. Also notice the spider plots, which try to visualize both maximum offset in a bin, and the range of azimuths going into that bin (which could be important for stress analysis, for example):</p>

<p><img src="https://i.sstatic.net/24MS0.png" alt="Spider plot for a seismic survey"></p>

<p>It's hard to go into a lot more detail, other than pointing at more things to read. There are a couple of really good books on this subject:</p>

<ul>
<li><a href="https://books.google.ca/books/about/Planning_Land_3_D_Seismic_Surveys.html?id=ZrqnAKuD44gC&amp;redir_esc=y" rel="nofollow noreferrer">Cordsen et al. (2000), <em>Planning Land 3D Seismic Surveys.</em> SEG Books.</a></li>
<li><a href="https://books.google.ca/books/about/3D_Seismic_Survey_Design.html?id=tRMiJ94mZE0C&amp;hl=en" rel="nofollow noreferrer">Vermeer &amp; Beasley (2012). <em>3D Seismic Survey Design.</em> SEG Books.</a></li>
</ul>

<p>For a quick overview, I recommend reading this great paper by Norm Cooper:</p>

<ul>
<li>Cooper, N (2004). A world of reality—designing land 3D programs for signal, noise, and prestack migration: a 2-part tutorial. <em>The Leading Edge</em> <strong>23</strong>, October and December, <a href="http://dx.doi.org/10.1190/1.1813357" rel="nofollow noreferrer">DOI:10.1190/1.1813357</a> and <a href="http://dx.doi.org/10.1190/leedff.23.1230_1" rel="nofollow noreferrer">DOI:10.1190/leedff.23.1230_1</a>.</li>
</ul>

CC BY-SA 3.0
2015-05-22T13:26:57.627Z
Takes me back :-) I don't know msw either but when I was in the industry, we were using a lot of very long offsets (8km+) in an attempt to image under the basalt lavas West of Shetland. So geology also plays a part.
winwaed
CC BY-SA 3.0
2015-05-24T11:57:44.290Z
thanks @kwinkunks for your answer.On a similar note is there any process for choosing which of the following transforms f-k,f-v,f-x,t-x...... would provide most correct interpretation?.
shrey
CC BY-SA 3.0
2015-05-22T12:59:41.327Z
2015-05-22T13:29:37.937Z
2015-05-22T13:29:37.937Z
Matt Hall
<p>I was going through a report on MASW (Multi Station Analysis of Surface Wave) and found this </p>

<blockquote>
  <p>"To avoid the aliasing in the space domain, geophone spacing (Δx) needs to be less than half of the minimum wavelength of interest but channels of the seismograph are limited. As a consequence, geophone spread length (L) is constrained in a certain range. However, on the other hand, a sufficient geophone spread is required for mode separation and the investigation depth."</p>
</blockquote>

<p>I understand that this may depend a lot on optimization but is there any approach or research which can be used to make this decision considering both small and large offsets might be useful based on what we are trying to determine.</p>

CC BY-SA 3.0
2015-05-22T13:04:25.073Z
Not sure how much of my answer is relevant to MASW. I'll delete it if someone comes up with something more direct.
Matt Hall
CC BY-SA 3.0
2015-05-27T07:53:51.740Z
Briefly: use as large receiver spread length as possible, but remember to keep your geophone spacing small enough. You may want to take a look at [_these tables_](http://masw.com/ACQParaTables.html), with best acquisition parameters for a given depth of investigation. And a "must-read" thing for anyone dealing with MASW is [_Claudio Strobbia's PhD thesis_](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.129.9410&rep=rep1&type=pdf) with lots of useful results and descriptions. My advice is definitely not as fundamental as the answer by @kwinkunks , so I add this as a comment :)
antongrin
<geophysics><seismology><waves>
How does one determine the optimum offset in a seismic survey?
shrey
# How does one determine the optimum offset in a seismic survey?

(Asked by: username_0 on 2015-05-21)

I was going through a report on MASW (Multi Station Analysis of Surface Wave) and found this

> "To avoid the aliasing in the space domain, geophone spacing (Δx) needs to be less than half of the minimum wavelength of interest but channels of the seismograph are limited. As a consequence, geophone spread length (L) is constrained in a certain range. However, on the other hand, a sufficient geophone spread is required for mode separation and the investigation depth."

I understand that this may depend a lot on optimization but is there any approach or research which can be used to make this decision considering both small and large offsets might be useful based on what we are trying to determine.

**Tags:** geophysics, seismology, waves

> **Comments:**
> **username_1**: Not sure how much of my answer is relevant to MASW. I'll delete it if someone comes up with something more direct.  
> **username_2**: Briefly: use as large receiver spread length as possible, but remember to keep your geophone spacing small enough. You may want to take a look at [_these tables_](http://masw.com/ACQParaTables.html), with best acquisition parameters for a given depth of investigation. And a "must-read" thing for anyone dealing with MASW is [_Claudio Strobbia's PhD thesis_](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.129.9410&rep=rep1&type=pdf) with lots of useful results and descriptions. My advice is definitely not as fundamental as the answer by @kwinkunks , so I add this as a comment :)  

---

## 1 answers

### Answer by username_1 on 2015-05-22. Score: 5 | Accepted answer

**It depends.**

Caveat: my experience is with reflection seismic surveys, but I think many of the principles are similar to MASW.

As you guessed: it's an optimization problem. There are lots of factors at play. It's up to the geophysicist to balance the various needs of the survey:

* You need to image the target with useful accuracy (small natural bin size).
* You want useful signal:noise levels (high fold and trace density).
* You want near offsets for good estimates of P-wave reflectivity.
* You want far offsets for good estimates of elastic properties (e.g. density).
* You may need far offsets to image certain types of geology.
* You want the acquisition crew to have enough receivers for the design.
* You want to be able to afford the acquisition and processing!

A while ago, I wrote a blog post on the subject: *[Fold for sale](http://www.agilegeoscience.com/blog/2012/9/6/fold-for-sale.html)*. It's about balancing fold (how many traces go into the stack, basically, a big driver of signal:noise) with cost.

My colleague Evan Bianco and I also did a series on modelling seismic acquisition. If you're into Python at all, there's some code to play with:

* *[The race for useful offsets](http://www.agilegeoscience.com/blog/2014/12/11/the-race-for-useful-offsets.html)*
* *[Laying out a seismic survey](http://www.agilegeoscience.com/blog/2014/12/17/laying-out-a-seismic-survey.html)*
* *[It goes in the bin](http://www.agilegeoscience.com/blog/2015/1/8/it-goes-in-the-bin)*
* *[Seismic survey layout: from theory to practice](http://www.agilegeoscience.com/blog/2015/1/14/seismic-survey-layout-from-theory-to-practice)*

The greatest minimum offset in a bin is an important consideration, as you guessed. Also notice the spider plots, which try to visualize both maximum offset in a bin, and the range of azimuths going into that bin (which could be important for stress analysis, for example):

![Spider plot for a seismic survey](https://i.sstatic.net/24MS0.png)

It's hard to go into a lot more detail, other than pointing at more things to read. There are a couple of really good books on this subject:

* [Cordsen et al. (2000), *Planning Land 3D Seismic Surveys.* SEG Books.](https://books.google.ca/books/about/Planning_Land_3_D_Seismic_Surveys.html?id=ZrqnAKuD44gC&redir_esc=y)
* [Vermeer & Beasley (2012). *3D Seismic Survey Design.* SEG Books.](https://books.google.ca/books/about/3D_Seismic_Survey_Design.html?id=tRMiJ94mZE0C&hl=en)

For a quick overview, I recommend reading this great paper by Norm Cooper:

* Cooper, N (2004). A world of reality—designing land 3D programs for signal, noise, and prestack migration: a 2-part tutorial. *The Leading Edge* **23**, October and December, [DOI:10.1190/1.1813357](http://dx.doi.org/10.1190/1.1813357) and [DOI:10.1190/leedff.23.1230\_1](http://dx.doi.org/10.1190/leedff.23.1230_1).

> **Comments:**
> **username_3**: Takes me back :-) I don't know msw either but when I was in the industry, we were using a lot of very long offsets (8km+) in an attempt to image under the basalt lavas West of Shetland. So geology also plays a part.  
> **username_0**: thanks @kwinkunks for your answer.On a similar note is there any process for choosing which of the following transforms f-k,f-v,f-x,t-x...... would provide most correct interpretation?.  

---

