A success for the launch of the SMAP satellite to monitor soil humidity

The SMAP satellite lifting off atop a Delta II rocket (Photo NASA/Bill Ingalls)
The SMAP satellite lifting off atop a Delta II rocket (Photo NASA/Bill Ingalls)

The SMAP (Soil Moisture Active Passive) satellite was launched on a Delta II rocket from Space Launch Complex 2 7320-10LC (SLC-2) of the base of Vandenberg, California. The spacecraft successfully separated from the rocket’s last stage after almost an hour and was placed in a sun-synchronous almost polar orbit that will have an altitude between 660 and 685 km (between 410 and 426 miles).

The SMAP satellite is an observatory that has the purpose of monitoring the moisture present in the top 5 centimeters (2 inches) of soil. It seems paradoxical to make measurements of this kind from the orbit but it makes sense if you think that SMAP will cover the Earth’s surface so as to be able to repeat its measurements about every three days.

The surface layer of the soil is the one in which vegetation grows, including the food we eat. The humidity in that layer is only 0.001% of the Earth’s water and yet strongly influences the state of vegetation and crops. Consequently, monitoring soil moisture allows obtaining important information on the status of what’s growing on it.

To perform its findings, the SMAP satellite will use a system of instruments consisting of a radiometer and a radar. Their configuration is unique because for the collection of data will use a rotating mesh reflector with a diameter of 6 meters (about 20 feet) that will be deployed in orbit.

The radiometer will provide accurate readings of moisture present in the top 5 cm surface soil but every single measurement will cover a large area. The radar will provide an image that can cover a smaller area but with less accuracy in the moisture measurement. SMAP will combine the observations of the two instruments to obtain accurate measurements of small soil areas.

The measurements of the SMAP satellite will help to monitor droughts, predict floods, assist agriculture, will provide more details of the water, energy, and carbon cycles, and will also help to improve weather forecasts. There are other satellites and various instruments that monitor the environment and all data will be combined. For example, there will be a synergy between SMAP and the OCO-2 satellite to study the connections between the cycles of water and carbon. This will also be useful to improve climate models.

There will be a long test phase to deploy the huge mesh reflector and especially to calibrate the instruments. If all goes well, the mission of the SMAP satellite should begin after 90 days. Its primary mission should last 3 years.

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