 # Open Grain Storage: Measuring Commodoties

Understanding and predicting commodity supply requires a wide variety of data points and an understanding of what is stored and where.

Using satellite data it is possible to calculate the yield of crops, location and storage volume of commodities (e.g grain, sugar, wheat) and even the intensity of delivery vehicles to and from storage depots.

The article below explains how satellite data can be used to calculate the storage volume of grain in an open warehouse – PDF version here. In countries with the appropriate climate,- hot and dry –  grains such as wheat can be stored outside in open warehouses. This is commonly seen in regions such as the Middle East and Africa,

These warehouses are ideal candidates for surveillance by satellites, as the pictures can be taken 15~+ times a day giving detailed updates on the volume of storage and reporting any storage.

However, looking at a simple picture of the grain does not tell the full story – it does not provide the height and therefore the volume cannot be calculated.

Calculating the volume of grain stored requires a combination of high-quality satellite images, physics, and a little trigonometry.

Grain is put into a storage pile at a warehouse either by movable elevators or by catapulting it in. As the grain is added a natural slope will form – known as an ‘angle of repose’.  This angle is determined by the friction between individual grains and varies with the structure and size of different grains  – there are databases of this information available.

Knowing the angle of repose and length of the storage pile means that accurate estimates of the volume of grains can be made The area of the grain is calculated by simply measuring the size of the sides of the grain. This can be automated to be conducted on a scale and at speed – using polygons for ease of use

Calculating the height of the grain pile is done by trigonometry.

• Measure the projected slope in the image (Step 3)
• 20m (in this instance)
• Estimate the angle of response
• 25° based on the standard tables
• Trigonometry to calculate the height
• 9.3m Examples of repose angle for different grains The volume of grain can be calculated by the following steps

1. Acquire current image
2. Calculate the area of each pile (see above)
3. Calculate the height of pile (see above)
4. Multiple the area by the height to get volume
5. Correct volume – allowing for the slope 