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 <[email protected]>
~25 Total