---
title: "AVO Screening (Part 4): AVO Product and Reflection coefficient difference"
description: "AVO Screening (Part 4): AVO Product and Reflection coefficient difference"
---

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# [AVO Screening (Part 4): AVO Product and Reflection coefficient difference](https://blog.geoteric.com/technical/part4-avo-screening)

 Written by [Luis Gomez](https://blog.geoteric.com/technical/author/luis-gomez) | Jun 4, 2015 8:30:00 AM

Gradient and Intercept volumes can be generated from the angle stacks as discussed in Part 3. The Gradient and Intercept volumes can be combined in a number of ways to generate different AVO attributes, such as AVO Product or Reflection coefficient difference. 

## AVO Product

The AVO Product is simply Gradient * Intercept. It has been found to nicely highlight **AVO class III responses** (Rutherford & Williams, 1989). Soft sands with hydrocarbons will have a strong negative intercept and a strong negative gradient, so they will show a strong positive response in the AVO product. Non-hydrocarbon bearing areas will be weak or have negative products (Avseth et al., 2010)  
   
The AVO product can be calculated in GeoTeric simply using the Parser expression:   
 

**(im1*im2)/scale**  
where im1=gradient and im2=intercept. 

   
The scale factor will need to be adjusted depending on the data type and dynamic range of the input volumes.

 

<https://blog.geoteric.com/hubfs/Imported_Blog_Media/avopro-2.png>

*AVO Product showing a class III anomaly in the Rosewall-Calliance dataset*

 

## Reflection coefficient difference

Castagna and Smith (1994) compared different AVO attributes, and found that the reflection coefficient difference, Rp - Rs, might be a better gas-sand discriminator than the AVO product, because it will work for any type of sand, whether these are **AVO class I, II or III**. They verified that Rp - Rscan be expressed in terms of intercept and gradient as follows:  
 

**Rp- Rs ≈ (R(0) + G)/2**

   
Or in Geoteric’s Parser language:  
 

**(im1+im2)/2**  
where im1=gradient and im2=intercept.

Previous posts in this series can be found here:   
[Part 1 AVO Screening :Difference and ratio volumes](https://blog.geoteric.com/technical/2015/04/23/avo-screening-part-1-difference-and-ratio-volumes)  
[Part 2 AVO Screening: AVO colour blends](https://blog.geoteric.com/technical/2015/05/08/avo-screening-part-2-avo-colour-blends)  
[Part 3 AVO Screening: Gradient and Intercept volumes](https://blog.geoteric.com/technical/2015/05/21/avo-screening-part-3-gradient-and-intercept-volumes)

[Part 5  we will look at AVO Screening: scaled reflectivity](https://blog.geoteric.com/technical/2015/06/16/avo-screening-part-5-scaled-reflectivity)

[View full post](https://blog.geoteric.com/technical/part4-avo-screening)

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