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Tim, What is your experiance with Neutron Probes? --- Begin Included Message --- On Mon, 14 Oct 1996 16:43:44 +1000 Hortech Services Pty Ltd wrote: > The sphere of influence of the neutron probe will vary with; > 1. THE DRYING CYCLE OF SOIL > 2. SANDY SOIL compared to CLAY SOIL > 3. DUPLEX SOIL or DRY TOP SOIL/WET SUBSOIL I would agree that all of this is true and therefore ..... > How reliable does this make a Neutron probe when close to soil surface ? > NOT AT ALL! Not only is it unreliable but it is also a safety hazard. > AND Is having a LARGE SPHERE OF INFLUENCE AND ADVANTAGE OR DISADVANTAGE ? Now this depends on what you want the information for. If the soil moisture profile is heterogenous, due to frequent wetting / drying cycles, then estimation of profile moisture content by point measurements is likely ot have a high degree of error. In this case the 'smoothing' effect of the large sphere of influence is a positive advantage. If you want to know the shape of that heterogenous profile, then the large sphere of influence makes the neutron probe the wrong tool for the job. --------------------------------------------------------------------- Tim Hess Department of Water Management Silsoe College Cranfield University Silsoe Tel (0)1525 863292 Bedford, MK45 4DT Fax (0)1525 863000 UK e-mail t.hess@cranfield.ac.uk http://www.cranfield.ac.uk/safe/people/thess.htm ---------------------------------------------------------------------- --- End Included Message --- ******************************************************** Dean Reynolds Associate Land and Water Use Analyst California Department of Water Resources 3251 S Street Sacramento, Ca. 95816 916-227-7602 916-227-7600 Fax dreynold@water.ca.gov