Ecosystem Scale Measurements of Water Using Cosmic-ray Neutrons Trenton Franz CUASHI Spring Seminar, March 29th, 2013 Department of Hydrology and Water Resources, University of Arizona With acknowledgements to COSMOS project Members and Collaborators: M. Zreda, TPA Ferré, C. Zweck, R. Rosolem, W.J. Shuttleworth, X. Zeng, S. Stillman, A. Karczynski, B. Chrisman, D. Desilets, S. Papuga, H. Adams, T. Kolb, B. Hornbuckle, S. Irvin NSF, Hydroinnova, Questa Instruments, Dualem, Acclima, Santa Rita Experimental Range Motivation Grand Challenge Issued to Global Land Surface Modeling Community (Wood et al., 2011) Land surface models at 1 km scale (currently 10-100 km)! Ability to monitor and predict Earth’s terrestrial water, energy, and biogeochemical cycles 2 Motivation Grand Challenge Issued to Global Land Surface Modeling Community (Wood et al., 2011) Land surface models at 1 km scale (currently 10-100 km)! Ability to monitor and predict Earth’s terrestrial water, energy, and biogeochemical cycles Critical for: Global food production Water resources suitability Flood and droughts Climate change prediction Photograph: Central Kenya July 2006 3 How can we do it? Computational needs: § Massively parallel computers currently capable of solving up to 109 unknowns 4 How can we do it? Computational needs: § Massively parallel computers currently capable of solving up to 109 unknowns Data needs: § More limiting than computational requirements § High resolution spatiotemporal forcing data available (NCEP reanalysis, statistical downscaling etc.) § Remote sensing products for biomass (NDVI 1km) § Clearly data needs for biogeochemical cycling 5 Outline 1. Introduce the new cosmic-ray neutron probe and COSMOS project 2. Area-averaged soil moisture measurements in the near surface 3. Recent work on separating pools of water and mobile measurements Robinson et al. 2008 6 Ecosystem Measurements § Energy, Water, and Carbon fluxes measured at intermediate scales with eddy covariance techniques Tonzi Ranch, CA June 2011 7 Ecosystem Measurements § Energy, Water, and Carbon fluxes measured at intermediate scales with eddy covariance techniques § Point measurements of soil moisture not necessarily representative of footprint Tonzi Ranch, CA June 2011 8 Ecosystem Measurements § Energy, Water, and Carbon fluxes measured at intermediate scales with eddy covariance techniques § Point measurements of soil moisture not necessarily representative of footprint § Direct soil moisture measurements at spatial scale time consuming and difficult Tonzi Ranch, CA June 2011 9 Ecosystem Measurements § Energy, Water, and Carbon fluxes measured at intermediate scales with eddy covariance techniques § Point measurements of soil moisture not necessarily representative of footprint § Direct soil moisture measurements at spatial scale time consuming and difficult § Critical link between water and energy balance is latent energy flux Tonzi Ranch, CA June 2011 10 Variations in Soil Moisture Collected over 200 m radius Mana Road Iowa 17 June 2010 September 2010 5 5 10 10 15 15 Depth,cm Depth,cm 20 20 25 30 25 5 10 15 20 25 30 35 20 25 30 35 40 45 50 Water content, vol. % Soil moisture, vol. % 11 Variations in Soil Moisture 4 10 16 22 vol. % 20 30 40 vol. % 5 15 25 35 vol. % 15 25 35 vol. % 5 10 15 20 vol. % 5 10 15 20 vol. % 2 4 6 8 vol. % 0 Sterling SMAP-OK 16 Sep 10 SMAP-OK 16 Sep 10 10 20 Jul 10 ARM-1 SMAP-OK Santa Rita 22 Jul 10 23 Jul 10 10 Oct 10 Depth, cm 20 Iowa Sep 10 30 5 15 25 35 vol. % 10 20 30 vol. % 2 4 6 8 wt. % 5 15 25 vol. % 15 30 45 vol. % 3 6 9 vol. % 6 9 12 15 wt. % 0 Toulouse Island 2 Mar 11 Mana Dairy Manitou Road 10 15 Jun 10 26 Jul 10 17 Jun 10 Depth, cm 20 Rancho no tengo Santa Rita Kendall 22 Aug 10 6 Jan 11 29 Aug 10 30 5 10 15 20 wt. % 20 30 40 vol. % 5 10 15 20 vol. % 20 30 40 vol. % 30 40 50 vol. % 30 35 40 45 vol. % 20 30 40 50 vol. % 0 Riet- Desert holz- Chaparral bach 10 8 Mar 11 11 Apr 11 Marshall Mozark Morgan 23 Oct 09 Coastal 18 Apr 11 Monroe Depth, cm 20 Sage 24 Mar 11 9 Mar 11 Neb 3 23 Apr 11 30 0 2 4 6 wt. % 10 20 30 wt. % 5 10 15 20 wt. % 2 4 6 8 wt. % 5 15 wt. % 25 5 15 25 vol. % 5 10 15 20 vol. % 0 San Pedro San Pedro San Pedro 3 Apr 10 7 Jul 07 12 Nov 09 10 San Pedro San Pedro Depth, cm 20 9 Aug 07 6 Dec 08 San Pedro San Pedro 12 Feb 10 5 Mar 10 30 5 15 25 wt. % 5 10 15 20 vol. % 15 20 25 30 wt. % 20 30 40 50 vol. % 10 20 30 40 vol. % 20 30 40 vol. % 35 40 45 vol. % 0 Harvard 10 Park Falls 2 May 11 Metolius 20 Jul 11 Tonzi 14 Jun 11 Bondville 11 May 11 Chestnut 25 Mar 11 Howland Depth, cm 21 Mar 11 20 4 May 11 30 12 Measurements of Soil Moisture TDR Sensor Array 1 year 1 month 1 day 1 hour 1 minute 1 m 100 m 10 km 1000 km Adapted from Robinson et al. 2008 13 Measurements of Soil Moisture TDR Sensor Array Satellite Remote Sensing 1 year 1 month 1 day Airborne Remote Sensing 1 hour 1 minute 1 m 100 m 10 km 1000 km Adapted from Robinson et al. 2008 14 Measurements of Soil Moisture TDR Sensor Array Satellite Remote Sensing Mobile TDR & EM 1 year 1 month 1 day Airborne Remote Sensing 1 hour 1 minute 1 m 100 m 10 km 1000 km Adapted from Robinson et al. 2008 15 Measurements of Soil Moisture TDR Sensor Array Satellite Remote Sensing Mobile TDR & EM 1 year 1 month 1 day Airborne Remote Sensing 1 hour Cosmic-ray Probe and Rover 1 minute 1 m 100 m 10 km 1000 km Adapted from Robinson et al. 2008 16 COSMOS Project COsmic-ray Soil Moisture Observing System (COSMOS) Phase I: NSF project 2009-2013, ~50 US Probes Phase II: Expansion to 500 probes 17 COSMOS Project COsmic-ray Soil Moisture Observing System (COSMOS) Phase I: NSF project 2009-2013, ~50 US Probes Phase II: Expansion to 500 probes Science Priorities: § Soil moisture controls: § weather and climate models § ecological processes and phenomena § hydrological flow processes in catchments § Water storage on/in vegetation canopies § Frozen precipitation § Remotely sensed measurements of soil moisture 18 COSMOS Project Status § COSMOS data freely available at http://cosmos.hwr.arizona.edu/, some quality control, usually co-located with eddy covariance towers § Probes: 60 COSMOS, 60 Independent networks around globe (CosmOz, TERENO, etc.), ~100 more to come online soon (1 yr) 19 Cosmic-ray Neutrons Above the Surface 600 July - August 1964 April - May 1965 500 400 dry earth 300 water 200 Height in air (meters) Height 100 0 1 10 Hendrick and Edge, 1966 Neutrons (10-7 cm-2 sec-1 eV-1) 20 Production of Secondary Particles 0 200 ) -2 400 600 z coordinate (g cm (g z coordinate 800 1000 -600 -400 -200 0 200 400 x coordinate (g cm-2) Secondary cosmic-ray particles Cascade initiated by a 10 GeV primary. All produced in copper plates in a trajectories above 1 MeV are shown. large cloud chamber. (Simulations courtesy of D. Desilets, Skobeltzyn, 1927 Sandia National Laboratories) 21 Cosmic-rays on Earth Space: • Primary - mostly protons and alphas incoming high- • Interact with magnetic field energy cosmic-ray proton - intensity depends on geomagnetic latitude • Interact with atmospheric nuclei Atmosphere: • Produce secondary particles - cascade generation of - intensity depends on barometric secondary cosmic pressure rays • Produce fast neutrons - slowing down by elastic collisions - leads to thermalization - and then absorption Ground: scattering The last three processes depend on the thermalization chemical composition of the medium, in absorption particular on its hydrogen content Summarized in Zreda et al., 2012 22 Elements: What We See Nucleus size H 23 Elements: What Neutrons See Scattering cross-section Gd 24 Elements: What Slows Neutrons Logarithmic energy decrement per collision 25 Elements: What Stops Neutrons Stopping power Stopping Element Power H 22.016 C 0.875 O 0.508 Fe 0.411 Mg 0.297 Na 0.277 Si 0.151 Ca 0.139 Al 0.109 K 0.099 26 Neutron Response to Soil Moisture 5000 SiO , N = 1000 cph 4500 2 S 4000 3500 3000 2500 2000 1500 Modeled Neutron Counts (cph) 1000 0 5 10 15 20 25 30 35 40 45 Mean Soil Moisture (Vol. %) 27 Summary of Key Neutron Properties 1. 8.5:1 difference in fast neutron intensity between dry soil and water (Hendrick and Edge, 1966), see ~3:1 different for natural soil moisture variations Desilets, 2011 28 Summary of Key Neutron Properties 1. 8.5:1 difference in fast neutron intensity between dry soil and water (Hendrick and Edge, 1966), see ~3:1 different for natural soil moisture variations 2. Hydrogen has stopping power 25 times greater than other major elements present (Zreda et al., 2008 & 2012) Desilets, 2011 29 Summary of Key Neutron Properties 1. 8.5:1 difference in fast neutron intensity between dry soil and water (Hendrick and Edge, 1966), see ~3:1 different for natural soil moisture variations 2. Hydrogen has stopping power 25 times greater than other major elements present (Zreda et al., 2008 & 2012) 3. Neutron average jump length in air ~30 m, average between 20 to 60 collisions over energy range (~107 to 10 eV), neutron velocity > 10 km s-1 (Desilets, 2011 and Glasstone, 1952) Desilets, 2011 30 Key Assumption Therefore assume well-mixed neutron density in air where nature performs averaging and we can sample system at a point! 31 Cosmic-ray Probe 32 Cosmic-ray Probe in the Field Marshall Lake, CO, Oct 2009, D.