1 Read the short article below about soil moisture:

What is Soil Moisture?
Soil moisture is difficult to define because it means different things in different disciplines. For example, a farmer's concept of soil moisture is different from that of a water resource manager or a weather forecaster. Generally, however, soil moisture is the water that is held in the spaces between soil particles. Surface soil moisture is the water that is in the upper 5 to 10 cm of soil, whereas root zone soil moisture is the water that is available to plants, which is generally considered to be in the upper 200 cm of soil.

Why is Measuring Soil Moisture Important?
Compared to other components of the hydrologic cycle, the volume of soil moisture is small; nonetheless, it is of fundamental importance to many hydrological, biological and biogeochemical processes. Soil moisture information is valuable to a wide range of government agencies and private companies concerned with weather and climate, runoff potential and flood control, soil erosion and slope failure, reservoir management, geotechnical engineering, and water quality.

Soil moisture is a key variable in controlling the exchange of water and heat energy between the land surface and the atmosphere through evaporation and plant transpiration. As a result, soil moisture plays an important role in the development of weather patterns and the production of precipitation. Simulations with numerical weather prediction models have shown that improved characterization of surface soil moisture, vegetation, and temperature can lead to significant forecast improvements. Soil moisture also strongly affects the amount of precipitation that runs off into nearby streams and rivers. Large-scale dry or wet surface regions have been observed to impart positive feedback on subsequent precipitation patterns, such as in the extreme conditions over the central U.S. during the 1988 drought and the 1993 floods. Soil moisture information can be used for reservoir management, early warning of droughts, irrigation scheduling, and crop yield forecasting.

Soil water serves as a carrier of food nutrients for plant growth. In fact, plant biomass for a given area is more often determined by the amount of water available rather than the deficiency of other food nutrients for a variety of reasons:

• Soil water acts as a nutrient itself;

• Soil water regulates soil temperature;

• Soil forming processes and weathering depend on water;

• Microorganisms require water for their metabolic activities;

• Soil water helps in chemical and biological activities of soil;

• It is a principal constituent of the growing plant; and

• Water is essential for photosynthesis.

2 Watch the following video to learn more about NASA's SMAP Program, which measures soil moisture using remote sensing:

You can also visit the SMAP website.

After watching the video, your instructor will lead a class discussion on the importance of globally scaled soil moisture data and the importance of validating large-scale data sets like that produced by SMAP.

Visit the Globe website to learn about how schools and colleges can participate in validating large-scale data sets. With the help of your instructor, review and interact with the SMAP page of the website so you know how to navigate through it and upload your own data after you collect it.

3 Understand the importance of validating remote sensing data

Inferring conditions about the earth’s surface using remotely sensed measurements almost always requires the use of reference, or “ground truth” data, in other words, data that is collected in the field. Those ground-based field measurements typically involve collecting measurements of the phenomena or target being remotely sensed, in this case soil moisture data, which will be used to help validate the remotely sensed SMAP data. Generally, ground-truth data is used to assist with (1) image analysis and interpretation (e.g. image classification) of remotely sensed imagery, (2) remote sensor calibration, and (3) accuracy assessment of image analysis results.

Much of the emphasis on collecting ground truth is for verification and assessment. When a remote sensing or image processing technique is under development, it is mandatory to have sufficient ground truth data to test not only the accuracy of the final image analysis output, but also the intermediate steps in that process. General guidance for ground truth collection in remote sensing research and development (R&D) is dependent on specifics of the technology being developed. By participating in this lab, you are (1) assisting NASA’s SMAP team as they develop the protocols for ground-truth data collection through the use of sensors and an app and (2) helping validate SMAP data.

4 Predict the impact of climate change on the growth and distribution of camas.

Your instructor will use several resources (a pdf on phytogeography of Camas, a pdf plant guide, and research by SKC students and faculty) to lead a discussion about the natural history of camas (Camassia quamash) and its soil moisture requirements.

Predict what the soil moisture conditions will be by printing the soil-moisture scale below and placing a mark on the spot that you think
best represents the soil moisture needs of camas. Make one mark for each of the four seasons. To print the scale, click on the printer icon at bottom right.