NASA Probe to Improve Climate and Weather Forecasting

from NASA

On January 31, 2015 NASA successfully launched the SMAP (Soil Moisture Active Passive) mission satellite.  The SMAP mission will provide global measurements of soil moisture and its freeze/thaw cycle from a near-polar sun-synchronous orbit. The plan is for SMAP to measure soil moisture every 2-3 days over at least a three year mission.

The SMAP mission will provide global mapping and monitoring of landscape freeze/thaw cycle and surface soil moisture content. The data will be used to model and estimate the earth carbon/ carbon dioxide fluxes and underlying environmental controls. Scientists hope that these observations will allow them to link together the terrestrial water, energy and carbon cycle processes and identify why the climate models have failed to predict the last 15 years of near stable global temperatures. Scientists hope to use this and other global data to identify the functioning of the “missing carbon sink” that has slowed the predicted rise in global temperatures. NASA hopes that SMAP will bring us some of the data we need to better understand our planet and predict its future. Though, the most immediate benefit will be drought prediction.

SMAP will accomplish its mission by measuring how much water is contained in the top layer of soil and identifying when the ground is frozen. This is accomplished using an instrument that combines an L-band radar and an L-band radiometer that both share a 6 meter in diameter aperture reflector. The reflector will rotate to scan a 621 mile wide swath of earth on each orbital pass of the observatory. The radiometer provides “passive” measurements of the microwave emissions of the upper soil. The radar makes the “active” back scatter measurements of the surface. Thus, the name of the mission- Soil Moisture Active Passive.

The ground processing systems run by the NASA Jet Propulsion Laboratory and the Goddard Space Flight Center will combine the data sets. Combining the active and passive datasets increases the resolution and accuracy of the data. Together the instruments will be able to measure the moisture in the top two inches of soil to a spacial resolution of under two miles.

The SMAP mission will also collect data on the frozen/thawed state of the soil. This information is important to understand the length of the plant growing season and will increase our understanding the contribution of the boreal forest to the global carbon balance and contribute to a better understanding of droughts and climate.

A high-resolution, space-based measurement of soil moisture is a new capability. Scientists will be able to better predict natural hazards of extreme weather, climate change, floods and droughts, and help reduce uncertainties and unknowns that now exist in our understanding of Earth's water, energy and carbon cycles. Several of the data gathering techniques grew out of previous NASA missions of this century including the Aquarius project and the cancelled Hydros project.

The microwave portion of the electromagnetic spectrum (wavelengths from a few centimeters to a meter) is used to estimate the surface soil moisture. Passive microwave sensors measure the natural thermal emission emanating from the soil surface. The intensity of this radiation depends on the dielectric properties and temperature of the target medium, which for the SMAP mission is the surface soil layer and is a function of the amount of moisture present. The low microwave frequencies used offer additional advantages; the atmosphere is almost transparent in that wavelength so weather does not impact the sensing, transmission of the data from the soil is also possible through sparse to moderate vegetation water content, and the microwaves measurements are not impacted by daylight to allow for 24 hour observations.

The SMAP mission will map the entire globe every two to three days for at least three years and provide the most accurate and highest-resolution maps of soil moisture ever obtained. The spacecraft's final circular polar orbit will be 426 miles (685 kilometers), at an inclination of 98.1 degrees. The spacecraft will orbit Earth once every 98.5 minutes and repeat the same ground track every eight days.

Weather forecasting, accurate modeling and forecast of climate variability and change, planning and predicting agricultural productivity, effective water resources management, drought prediction, flood area mapping, and ecosystem health monitoring all require information on the status of soil moisture. Soil moisture affects plant growth and agricultural productivity, especially during times of drought or water shortages. This can improve our ability to monitor and forecast agricultural productivity and allow for a famine early warning in the most food insecure regions of the earth.

GRACE Watches Building Water Crisis

Earlier this month Dr. Jay Famiglietti, a professor of Earth System Science at the University of California, Irvine, and Director of the UC Center for Hydrologic Modeling (UCCHM) and Matt Rodell, now Chief of the Hydrological Sciences Laboratory at NASA’s Goddard Space Flight Center have published an new paper in Science entitled, “Water in the Balance.” The scientists draw conclusions and trend from the ten years of data that has come from the Gravity Recovery and Climate Experiment (GRACE) and Global Land Data Assimilation System (GLDAS) to quantify groundwater depletion. A group of researchers at the University of California, Irvine, the University of Texas, and the Hydrological Sciences Branch at NASA GSFC have worked in partnership to apply GRACE and GLDAS to various real world groundwater monitoring.

GRACE data has provided a global picture of water storage trends for over a decade and could be an invaluable tool for understanding water resource availability. The GRACE mission is able to monitor monthly water storage changes within river basins and aquifers that are 77,000 square miles or larger. While this area may be too large for community water management, it can be used on the regional and national scale, and to aide international policy discussions. This information could someday be used to develop a unifying principal of cross border water resource allocation. Now, though, the first use has been to study the trends on groundwater in various regions during this period.

Stressed aquifers are in yellow, orange and red

Dr. Famiglietti points out that groundwater represents almost half of all drinking water worldwide, though a lesser proportion of irrigation water. In the United States groundwater is an important natural resource, representing about 30% of all consumptive water use especially in those parts of the country that don't have ample surface-water sources, such as the arid West and in times of drought. Groundwater is a renewable resource, but not in the way that sun light is. Groundwater recharges at various rates from precipitation. Changes in rainfall patterns and the actions of man can impact the recharge rate of groundwater. Increasing the amount of impermeable area by paving or building and other changes to land cover can reduce groundwater recharge. The climate of the planet has continually changed over the millennia and some groundwater aquifers are legacies of an earlier climate and are not being recharged.

To recharge groundwater, it must rain and the soil must be able to absorb the water. When you withdraw the groundwater from fine-grained compressible sediments and do not replace it, the land subsides. In the pursuit of wealth the ground water in the incredibly fertile Central Valley was pumped to such an extent that the ground subsided more than 75 feet in some places. The area was identified by the research efforts of Joseph Poland as the location of maximum subsidence in the United States due to groundwater mining. Once the land subsides, it loses its water holding capacity and will never recover as an aquifer. Groundwater mining in the Central Valley was believed to have slowed in the past few decades, but it continues as documented by the recent data from Drs. Famiglietti and Rodell’s work and the continual falling of the groundwater level.

Though, ten years of data may not be adequate to determine accurate changes in water availability and groundwater recharge. Using GRACE data, Drs. Famiglietti and Rodell identified what appear to be in this 10 year window water ‘hotspots’ in the United States, and these include the important food producing regions in California’s Central Valley, and the southern High Plains; large areas of the southeastern U. S. that has been plagued by persistent drought, including Houston, Texas, Alabama, and portions of the Mid-Atlantic region. Based on the data since 2003, the wetter, northern half of the U.S. has become wetter, while the drier, southern half has become generally drier.

Dr. Rodell hopes to have the next generation of satellites able to monitor groundwater changes on a weekly basis and to be able to monitor groundwater and river basins that are closer to 1,000 square miles in area. In addition, to have the resources to interpret the date in a more timely fashion so that communities can use it to manage water resources in real time. Our water resources are the urgent need. Water is life. We must develop sustainable water, economic and agricultural policies to ensure the certainty and security of our food supply and water supply. If the water use is not sustainable, then ultimately we are not sustainable on a much shorter scale than climate change.