RETMCL: Incorporating maximum-likelihood estimation principles in the RETCsoil hydraulic parameter estimation code

RETC is a public domain computer code for estimating parameters of the wate r retention curve and hydraulic conductivity functions of unsaturated soils . RETC was developed at the US Salinity Laboratory and is now used world-wi de with thousands of copies distributed. Evaluation of the final estimation results in the code has been improved to yield a new version, RETCML, base d on the maximum-likelihood theory for the special case of weighted least-s quares estimators. This paper first explains the theory of maximum-likeliho od and introduces the principles of model adequacy and parameter uncertaint y on a formal basis. Next, this paper presents a user guide for the code. R ETCML is also free and has been programmed to be almost fully compatible wi th the original RETC input files, thus making it easy to re-analyze previou s data. The output of RETCML includes a thorough evaluation of estimation r esults. (C) 2000 Elsevier Science Ltd. All rights reserved.