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The attempt was to develop a portable closed canopy chamber for the measurement of crop evapotranspiration, using transparent acrylic sheet of 4 mm thickness. The length, width and height of the chamber are 0.85 m, 0.85 m and 1.10 m respectively. Two small fans were mounted on the inner side of the chamber for proper mixing of air and water vapour inside the canopy chamber. Between the fans, a temperature and humidity sensor was suspended above the plant canopy for the measurement of instantaneous temperature and RH of vapour-air mixture. The calibration and validation of the developed closed canopy chamber were made using micro lysimeters having a size of 0.2 m × 0.2 m × 0.2 m by growing shallow rooted spinach crop in it. The irrigation applications to the spinach was made as per the crop water consumption. The sensor sensed and recorded the instantaneous temperature and relative humidity at 1 second interval during the 2 min closing time of each cycle of first 15 minutes of 12 period of 2h duration during a day. Between the measurements, the chamber over the micro-lysimeters was removed for a minimum of 2 min to obtain a micro-climate similar to the open atmosphere. Two sample t-tests were applied to compare the data pairs of crop evapotranspiration obtained by the micro-lysimeters inside the canopy chamber with that of outside the canopy chamber to ascertain whether there is any effects of the change in micro climate for a short period of 2 min on the crop growth physiological processes. Also, the data pair of crop evapotranspiration measured by the micro lysimeter and canopy chamber using the sensor data of temperature-humidity were compared and statistically analyzed through t-test. The calibration factor of the closed canopy chamber was found to be 1.3532. The results revealed that there was no significant difference in the crop evapotranspiration measured by the micro-lysimeters inside and outside the canopy chamber, indicating that there are no effects of the change in micro climate for a short period of 2 minutes in the chamber, on the plant physiological processes. The crop evapotranspiration measured by the canopy chamber and micro-lysimeter were compared separately for the winter and summer seasons. The ETc rate increases as sun rises and reaches the peak at 14:00 hrs and then continuously decreases with the time. The ETc rates were found to be very low and constant during the night time, indicating the major contribution is from the soil evaporation component. There were no significant difference between the crop evapotranspiration measured by the canopy chamber and the micro-lysimeter at 95 percent confidence level. The average crop coefficients for the initial stage, mid stage and harvest stage were found as 0.968, 1.187 and 1.07 respectively during the winter season. The developed canopy chamber is portable as well as more comfortable and cost effective compared to the lysimeter for the measurement of the actual crop evapotranspiration and the crop coefficient.