The crop coefficient (K_c) is an important parameter to estimate the actual field crop evapotranspiration (ET_c) relative to a standardized plant canopy unconstrained by available soil moisture and nutrients, disease or pests (i.e ET_o). However, splitting the evapotranspiration into its components of soil evaporation (E_s) and plant transpiration (T_r), an important step to better understand and manage the actual crop water requirement, is challenging. In this study a protocol has been developed to estimate K_c from proximal, active optical sensor (AOS) derived Normalized Difference Vegetation Index (NDVI) measurements. A polynomial regression (R²=0.86) was developed for the observed, multi-temporal, K_c-NDVI relationship derived using the coincident measurements of K_c and NDVI at two different stages of growth for a pasture (Festuca arundinacea var. Dovey) canopy. The K_c was calculated from field measurement of evapotranspiration with the help of a portable canopy evaporation chamber and the reference crop evapotranspiration (ET_o) data that was sourced from a nearby Automatic Weather Station (AWS). The portable enclosed chamber was calibrated beforehand to confirm the suitability of the device to measure the amount of water vapour produced by  a target pasture canopy as evapotranspiration, producing a calibration factor (C) close to 1 (C = 1.02, R² = 0.87). The protocol was implemented to separately derive transpiration and evaporation components through basal crop coefficient (K_cb) and evaporation coefficient (K_e) following the FAO dual crop coefficient approach; here the K_cb was correlated with corresponding leaf area index (LAI) values measured with a handheld optical LAI sensor (LAI Ceptometer). The ability to partition the soil evaporation component (K_e) from the transpiration component (K_cb) using a number of in-situ plant canopy surface coating methods were investigated. A commercially available anti transpirant coating (30-60% Acrylic polymer) has been found effective to stop the transpiration allowing the soil evaporation component to be isolated.