The COsmic-ray Soil Moisture Observing System (COSMOS):

New opportunity to explore carbon/water cycle links at AMERIFLUX sites

W. James Shuttleworth, Marek Zreda, Xubin Zeng, W. James Shuttleworth, Marek Zreda, Xubin Zeng, Chris Zweck, Ty P.A. Ferré and Rafael RosolemChris Zweck, Ty P.A. Ferré and Rafael Rosolem

Department of Hydrology and Water Resourcesand Department of Atmospheric Science

University of Arizona, USA

With acknowledgements to:With acknowledgements to:

Darin DesiletsDarin Desilets, Amy Rice, Russ Scott, and Chawn Harlow

NSFNSF, Army Research Office, and UA Water Sustainability Program

HydroinnovaHydroinnova, Zetetic InstituteZetetic Institute, Quaesta Instruments, General Electric, and PDT

(The Hydroinnova Consortium)

A (Very) Brief Overview of COSMOS

• The need for plot average soil moisture measurements

• How does the COSMOS soil moisture probe work?

• COSMOS project plans in the next year

• Observational partnership with AMERIFLUX

Hypothesis: water stored in the soil which entered from earlier precipitation can subsequently be made accessible to the atmosphere (often via plants) and influence the weather for several months by:

contributing to the water available for precipitation (recycling)

regional modification of downwind structure of the atmosphere

generating mesoscale circulations

Evidence in hydro-climate records

Lagged correlation

between soil moisture and

precipitation in Illinois

(Findell & Eltahir, 1997)

Soil Saturation condition ahead of summer rain

Meteorological need for soil moisture measurements

Influence not through recycling,rather through modified

downwind lapse rate (Beljaars, Betts etc, 1990s)

Potential Temperature

Cloud

Height

Potential Temperature

Height

Cloud

Dry adiabaticlapse rate

Moist adiabaticlapse rate

Environmental adiabaticlapse rate

Meteorological need for soil moisture measurements

Mississippi Floods in 1993 - modelMississippi Floods in 1993 - observation

Upgrade of ECMWF land model gave more realistic precipitation

GCM evidence of the influence of

soil moisture status on seasonal climate

The Global Land-Atmosphere Coupling Experiment (GLACE)

Average for 8 “best” models

Meteorological need for soil moisture measurements

Sample sub-catchments

using a moveable probe

COSMOS COSMOS ProbeProbe

Soil moisture patterns in catchment hydrology to study:

Their relationship to topography, soil depth, bedrock, permeability, and their covarianceTheir rate of change from wet state to a dry stateTheir value as an additional model calibration objective function Their links to GRACE satellite studies ……..etc……..

Hydrological need for soil moisture measurements

Fundamentally based on the common stomatal pathway for CO2 and H2O flux

Facilitated by the footprint for eddy flux and COSMOS probe measurements being about the same size

Eco-hydrological need for soil moisture measurements

How do COSMOS Probes Measure Soil Moisture?

Neither the basic idea nor basic sensor technology is new(important from standpoint of “readiness”)

Neutron detectors have been around since the 1950s.They are simple, robust, and stable, and are now available “off the shelf”.

What is New? systematic understanding of cosmic-ray neutron interactions at the ground-atmosphere interface (based on measurements and modeling) that identified the near- surface above-ground fast neutron density has:

i. a source footprint of hectometersii. limited sensitivity to soil type

improved and low power electronics (for pulse shaping and amplification; remote detection and correction of sensor drift, and remote data capture); and better (solar) power systems

Hendrick and Edge (1966) Cosmic-ray

neutrons near the Earth Physical

Review Series II, 145:1023-1025.

The fact that surface moisture can alter the measured above-ground neutron count rate was known in the 1960s

(and considered a nuisance!)

Dry soilDry soilMoist soilMoist soilWaterWater

How do COSMOS Probes Measure Soil Moisture?

How are high energy neutrons created in the soil?

IN SPACE: there are incoming high-energy cosmic-ray protons

Their intensity changes slowly with time, and with geomagnetic latitude,

(because they interact with the Earth’s magnetic field). These both

have to be corrected for in COSMOS

IN THE ATMOSPHERE: cascades of secondary cosmic rays are generated

The intensity of these cascades depends on barometric pressure. This

has to be corrected for in COSMOS

IN THE SOIL: the fast neutrons are scattered (“thermalized”) and

absorbed

BUT some escape back into the air above the ground, depending on the

composition of the soil,

especially on its water content(strictly hydrogen content)

Relative absorbing power

Relative “slowing” power

HydrogenHydrogen

HydrogenHydrogen

How do COSMOS Probes Measure Soil Moisture?

How does neutron count rate respond to soil moisture? Monte-Carlo Simulation of Neutron Density

Monte-Carlo Simulation of Neutron Density

In moister soil,less neutrons escape

In drier soil,more neutrons escape

COSMOS probes detect neutrons at two energies, but

use “fast” neutrons for soil moisture detection because

calibration is less sensitive to the chemistry of the soil

(thermal neutrons give information on above-ground

water, e.g. snow cover)Thermal Neutron Thermal Neutron

DetectorDetector

Fast Neutron Fast Neutron DetectorDetector

This is largely a soil-This is largely a soil-dependent “shift”,dependent “shift”,

SO ONLY ONE FIELD SO ONLY ONE FIELD CALIBRATE NEEDEDCALIBRATE NEEDED

How do COSMOS Probes Measure Soil Moisture?

Over what soil volume does the COSMOS probe measure?

Measurement VolumeMeasurement Volume(modeled by tracking neutron collisions)(modeled by tracking neutron collisions)

86% of neutrons from within a radius of 350 m

Independent of soil moisture

Increases with increasing altitude

(decreasing pressure)

86% of neutrons from within a depth of 70 cm

(dry)

Depth decreases to12 cm in wet soils

Independent of altitude (and pressure)

Depth Radius

Rel

ati

ve

nu

mb

er

of

co

un

ts

Modeled Modeled relationshiprelationship

Measured Measured Count RatesCount Rates

Approximate check on radius - move sensor away from the coast in Hawaii

Move sensor Move sensor away from coastaway from coast

How do COSMOS Probes Measure Soil Moisture?

Example COSMOS Data for the San Pedro Basin

Soil moisture from cosmic-ray neutron data compared with gravimetric samples

Gravimetric samples are in red, with sampling error

Day in July 2007

7 8 9 10 11 12 13 14 15 16 17 18 19 20

Gra

vim

etr

ic w

ate

r co

nte

nt

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Diurnal Cycles

(moisture redistribution)

How many point measurements are needed to get a similar

(2%) precision in area-average

soil moisture?

For the (single) calibration of a COSMOS probe

(made at installation), soil will be sampled

at 3 depths, 8 directions, and 3 radii

around the probe(i.e., 72 samples).

Looking to the Future

Large Scale COSMOS Deployments at up to 500 Sites

COSMOS Project Deployment Plans

COSMOS approved by NSF for 4 years (Sept 2009 – Aug 2013) operating in “proof of concept and demonstration of data utility mode”

Opportunity for a (10-fold?) expanded national network of COSMOS probes thereafter, subject to success in this initial phase

50 COSMOS probes will be deployed by the end of 2011 at sites selected to

provide maximum benefit to the scientific community

effectively demonstrate the value of this new measuring method

Need sites with ancillary open source meteorological data and fluxes

Currently Deployed Probes

Note additional Note additional AMERIFLUX sitesAMERIFLUX sites

(mainly Tilden Myers (mainly Tilden Myers

Additional Near-term Deployments

Jan 2011 May 2011

AMERIFLUX AMERIFLUX sitessites

COSMOS Project Deployment Plans

Additional AMERIFLUX Sites where COSMOS might be deployed this year

By Dec 2011

COSMOS Project Deployment Plans

2?

3+?

3+? 5+?

2+?

2?

2+?

By Dec 2011

Additional AMERIFLUX Sites where COSMOS might be deployed this year

~25 Total

Bottom Line The COsmic-ray Soil Moisture Observing System (COSMOS) Project is

urgently soliciting expressions of interest in collaborative research at AMERIFLUX sites to explore carbon/water cycle linkages

Must have publicly available measurements of meteorological variables and water vapor and CO2 fluxes

If interested, please:

take and complete an “expression of interest” form, and;

contact Rafael Rosolem <rosolem@email.arizona.edu>

~25 Total