Monitoring the Plant Density of Cotton with Remotely Sensed Data 3.3 The Validation of Estimated Models and Its Application The validation of estimation models.As Table 1 shows.the veracity of regression models from(6)to(14)is tested,all determination coefficients between the estimated and measured value are validated,but it is noticeable that the determination coeffi cients of I and IV from DEVI on May 24 also pas s through e significant testing The RMSE on PDC is 0.301x10 plant.hm and REPE is 27.1%,which indicates e mae D m RMsg0n plant.hm2,respectively,and REPE is 25.7%and 23.2%,respectively.However,the estimation accuracy of models is greatly improved on May 24th June h and June 25 when the data of middle emer nce stage is used to estimate PDC.Among them RMSE and REPE of /on June s the lowest value (x1000P90n Hectare s120 2 Fig.4.Monitoring PDC with remotely sensed data from LANDSAT-5 in the 148h farm of Xinjiang.chinaMonitoring the Plant Density of Cotton with Remotely Sensed Data 97 3.3 The Validation of Estimated Models and Its Application The validation of estimation models. As Table 1 shows, the veracity of regression models from (6) to (14) is tested, all determination coefficients between the estimated and measured value are validated, but it is noticeable that the determination coeffi￾cients of Ⅲ and Ⅳ from DEVI on May 24th also pass through the significant testing. The RMSE on PDC is 0.301×105 plant﹒hm-2 and REPE is 27.1%, which indicates that DEVI would bring the monitoring time forward, on the contrary, when EVI is used to estimate PDC on June 9th and June 25th, RMSE is 0.280 and 0.253×105 plant﹒hm-2, respectively, and REPE is 25.7% and 23.2%, respectively. However, the estimation accuracy of models is greatly improved on May 24th, June 9th and June 25th when the data of middle emergence stage is used to estimate PDC. Among them, RMSE and REPE of Ⅰon June 9th is the lowest value. Fig. 4. Monitoring PDC with remotely sensed data from LANDSAT-5 in the 148th farm of Xinjiang, china