the short - wave near - infrared ( sw - nir ) region , 7001100  nm , is suitable for nondestructive or noninvasive analysis of biological and biomedical materials [ 13 ] . compared with long - wave nir region ( 11002526  nm ) , the short - wave near - infrared can penetrate more deeply into a sample with less heating effect and in particular the interference arising from the intense water bands can be diminished . in practical , the low cost of sw - nir technology is a big advantage . the inexpensive tungsten lamps , leds , or the sunlight can be utilized as the sw - nir light source and the light can be transmitted through inexpensive glass optical fibers . moreover , the price of multichannel detectors , such as silicon charge - coupled device ( ccd ) and photo - diode array ( pda ) , is getting lower and lower with the increment of performances . ccd detector is a solid - state device , and the geometry and stability of the pixels are ultrastable . ccd - based spectrometers have advantages in terms of size , robustness ( no moving parts ) , and acquisition rate [ 5 , 6 ] . some commercial spectrometers are based on ccd technology ( e.g. , ocean optics and boston advanced technologies , inc . ) . thus , the sw - nir system based on ccd is cost effective for the comprehensive industry applications .   in the wine industry , the alcohol content level needs to be determined continually to resolute the end point of fermentation . alcohol meters are commonly used for this purpose . although the method is simple , inexpensive and free of other chemical , the disadvantages are obvious : ( 1 ) the required distillation is time consuming ; ( 2 ) a carefully calibration is needed according to temperature tables ; ( 3 ) it is sample consuming . the nir methods developed for alcohol determination have been reported in terms of beverages [ 7 , 8 ] , beer , and fuels . however , the nir method for alcohol determination in aqueous samples must take into account the influence of external variables such as temperature [ 11 , 12 ] . since the temperature can lead a change in the vibration spectra , a multivariable calibration model will not have good prediction ability without the temperature correction . several kinds of calibration strategies were reported for this purpose , such as global model building   and simulated annealing . some spectra standardization method , such as piecewise direct standardization ( pds ) , orthogonal signal correction ( osc ) , dynamic orthogonal projection ( dop ) , and generalized least squares weighting ( glsw ) , can also be utilized . these methods provide means to mitigate the effect of interference arising from background chemical or physical species , systematic sampling errors , and instrumental drift .   in this paper , a low cost and compact prototype of short - wave nir spectrometer module has been designed for the alcohol determination during wine fermentation . the testing results of signal - to - noise ratio , stray light level , and baseline stability were presented . the designed system was applied for alcohol determination in combination with partial least square ( pls ) calibration . ethanol aqueous solutions were prepared in concentration range from 30% to 70% ( v / v ) and determined at different temperatures . glsw method was utilized to correct the temperature effect and compared with the direct transfer calibration . the schematic diagram and the operation principle of the transmittance measurement were illustrated in figure 1 . as shown , the light source is located at the focus point of a concave mirror . the radiation from the light source is paralleled and directed to the sample cell ( 10  mm optical length ) to illuminate the sample . after that , the light is transmitted through a long - pass filter ( cut - off wavelength of 650  nm ) , focused , and transferred out through an exit slit . the output light is directed to a fixed grating monochromator , positioned to give the required wavelength scale , and then reflected accurately to the ccd . the led - enhanced light source was designed by assembling a tungsten lamp with two narrow - band leds centered at the wavelengths of 920  nm and 1020  nm . during operation the control electronics drive the tungsten lamp and the leds independently to enhance the long - wavelength intensity . they contain a convex lens , entrance slit , concave grating , and a reflectance mirror . the main optical specifications are a focal length of 48  mm , a grating groove frequency of 1200  mm , a numerical aperture of 0.6 , and detection array width of 24  mm . by using a si ccd ( model ilx511 ) , the maximum optical resolution is obtained of 0.24  nm with wavelengths ranging from 650 to 1100  nm . the typical integration time is 2  ms and can be regulated from 1  ms to 10 seconds . 20 samples were prepared at 25c in the concentration range of 30%70% ( v / v ) . they were split into two subsets , 10 pieces for calibration and 10 for validation . each sample in the validation set was split into 4 portions and saved at 15c , 25c , 35c , and 40c , respectively . transmittance nir spectra were recorded with an optical resolution of 1  nm and at the integration time of 20  ms , accumulating 16 scans . total 50 spectra were recorded , 10 for calibration set at 25c , 10 for validation set at 15c , 25c , 35c , and 40c , respectively . alcohol meter ( lm79-j10 , beijing , china ) was used for the reference method . the temperature was kept constant by using a thermometer immersed in the samples with a precision of 0.1c , and the samples were placed in water bath . matlab7.9 ( mathworks , inc . , natick , ma , usa ) with pls_toolbox 6.2 from eigenvector research inc . ( 3905 west eaglerock drive , wenatchee , wa 98801 , usa ; http://www.eigenvector.com/ ) was used for data processing . signal - to - noise ratio is the most important parameter of an nir spectrometer . it can be improved by enhancing the signal intensity or reducing the noise level . in this paper , the signal intensity was improved by controlling the ccd integration time and changing the light source spectrum characteristics . as shown in figure 2 , the signal intensity increased with the integration time . the intensity in some wavelengths reached maximum with the 500  ms integration time . in practical , the appropriate integration time can be resolved when any of the ccd pixels provided the maximum signal output . and the spectrum recorded in this integration time can be used as the background . however , as shown in figure 2 , the signal intensity was not consistent in the whole wavelength range . to enhance the signal level , especially in the region after 900  nm , it can be seen that the signal was significantly enhanced in the long - wavelength region ( the shadow region ) . the signal - to - noise ratio in the whole wavelength range was calculated and compared by recording the same spectrum for 20 times . the average intensity was calculated as the signal value and the variance as the noise level . as shown in figure 3(b ) and figure 3(c ) , the signal - to - noise level increased in the shadow region . the average signal - to - noise ratio of the whole spectrum rose from 460 to 500 , getting 9% increase . the spectrometer was calibrated by using lasers at 808  nm and 960  nm . monochromatic lights centered at 718  nm , 820  nm , 902  nm , 992  nm , and 1078  nm were used to test the wavelength accuracy and stray light of the spectrometer module . the typical band widths at half maximum of the five monochromatic lights were 8  nm . as seen in table 1 , standard deviations of the tested five wavelengths were under 0.22  nm ( n = 20 ) . the stray light was calculated as maximum value outside the  18  nm region , centered at the pass - band and presented in percent , relative to the peak of the spectrum . the stray light was found to range from 0.03% to 0.65% depending on the wavelength , as listed in table 1 . the unit - to - unit repeatability of stray light was better than 0.1% ( 2 ) for the tested wavelengths . the baseline stability of the developed spectrometer was tested by recording the baseline every five minutes during 100 minutes . the baseline was defined as the absorbance spectrum of air with itself as the background . it increased from 0.07  db to 0.12  db near 700  nm , while the shifting became very tiny in the region around 1000  nm . the variance of the recorded baselines ranged from 0.0087  db at 1017.2  nm to 0.0705  db at 641.8  nm with an average value of 0.0296  db . the main specifications of the developed sw - nir spectrometer were listed in table 2 . the nir spectra of ethanol aqueous solutions for various alcohol contents and temperatures were shown in figure 4 . the original spectra of four alcohol contents at 25c were illustrated in figure 4(a ) and in figure 4(b ) was the smoothed spectra based on a savitsky - golay filter . as shown , an increase in the alcohol content leads to increase of the intensity of the small band around 900  nm and decrease at 9501000  nm absorbance . as seen , the increase of temperature leads to increase of 9501000  nm absorbance and a shift to the short wavelength . figure 4(d ) shows the temperature effect to higher alcohol content ( 75% v / v ) at four temperatures . the analysis shows that there is a dependence of the bands on alcoholic content and that a temperature correction seems to be necessary for a more general calibration model . models at 25c were cross - validated by leave - one - out strategy , tested by using the 25c validation set , and then used to predict the validation set at other temperatures . the latent variable ( lv ) number was selected according to root mean square error of cross - validation ( rmsecv ) and the optimized value was 2 . as shown in table 3 , the two latent variables were selected , because more lvs did not produce significant differences in rmsecv but lead to a higher rmsep . the coefficient of determination ( r ) for 25c was 0.99 , which showed a quite satisfactory correlation . however , as shown , results were poor for the same validation set at other temperatures . it was possible to see in figure 6 the presence of systematic errors due to changes of temperature ( b , c , d , and e denote temperature of 15 , 25 , 35 , and 40c , resp . ) . as shown , a positive systematic error was found when the validation set was at the lower temperature than the calibration set , while a negative systematic error was found when the validation set temperature was higher . a transfer calibration method , glsw , was applied to arrange the temperature correction . calculating a filter matrix based on the differences between groups of samples which should otherwise be similar , glsw helps to downweight the differences and make the spectra of the same sample at different temperatures appear more similar . the glsw procedure was performed by building a glsw model using selected samples in every temperature . five samples were selected in each validation set according to the euclidean distance to build the glsw model . after that , all the samples were filtered by the glsw model , and a model was rebuilt using the filtered 25c calibration set . larger values decrease the effect of the filter , while smaller  applies more filtering . as shown in table 4 , 0.01 was the best value in this case , providing rmsep of 0.74 , 0.55 , 0.82 , and 0.89 ( % v / v ) for 15 , 25 , 35 , and 40c , respectively . as shown in figure 7 , after the glsw filter , good corrections for all the four temperatures were obtained , r for 15 , 25 , 35 , and 40c was 0.997 , 0.997 , 0.996 , and 0.996 , respectively . in terms of rmsep for 15 , 25 , 35 and 40c validation sets , 3.39% , 0.52% , 2.77% and 5.57% were obtained for no - temperature corrected model , respectively . while , for the model using glsw filter , far more superior results were obtained , 0.74% , 0.55% , 0.82% , and 0.89% , respectively , as shown in table 4 . and with this correction , the previously appeared systematic errors disappeared , as shown in figure 8 , indicating the use of glsw in this case , a good method to correct for eventual problems related to temperature effect . a multichannel short - wave nir spectrometer was developed based on ccd detection and tested for performance evaluation . by optimizing the light source design , the signal - to - noise ratio , which is the most important parameter of an nir spectrometer , kept higher values in the whole wavelength range . the possibility and accuracy for alcohol determination in wine industry by using this inexpensive spectrometer were verified . to avoid errors raised by different temperatures , the glsw was proved to be a satisfactory method with a view to decreasing errors in relation to direct transfer calibration .