Influence of sampling position and quantity of spectrum on nondestructive measurement in guava

It is important to select optimum spectra sampling position and quantity in noninvasive examination of guava based on near-infrared diffuse reflection. Firstly, 12 kinds of spectra were collected from top, equator and bottom, respectively, then models were built based on 1 spectrum in equator, average spectrum of 4 spectra in equator and average spectrum of 12 spectra all over the samples. The prediction results demonstrated that the model based on average spectrum of 12 spectra all over the samples was the best, with Rp=0.962, RMSEP=0.432; the model based on average spectrum of 4 spectra in equator was better, with Rp=0.793, RMSEP=0.588; the model based on 1 spectrum in equator was the worst, with Rp=0.687, RMSEP=0.438. At last, 23 wavelengths were derived through successive projections algorithm. The model based on the 23 wavelengths produced Rp=0.902, RMSEP=0.438. As a result, the average transmission spectra all over top, equator and bottom contain the sample internal quality information adequately. The model based on the all over average spectrum had better result than the models based on single point or average spectrum over single district.