Instrument comparisons

With the former instrument, comparison is made with a double disc of yellow glass of definite depth of colour (standard colour), and when a 100 mm. layer of a liquid corresponds in colour with the standard, the colour of the liquid is taken as 1 thus, the colour of any liquid is obtained by dividing 100 by the depth in mm. of the layer necessary to equal the standard colour. The value obtained is then referred to 100 of pure sugar, allowance being made for the sugar content of the juice and for the extent to which it is diluted for the determination of the colour. 

Myhre et al. (2004, 2005) performed comparisons of retrieval algorithms for AOT over the ocean using the data of satellite observations for 8 months (November 1996-June 1997) made with the AVHRR, OCTS, POLDER, and TOMS instrumentation. Comparisons revealed the presence of considerable differences (by a factor of 2 and more) between retrieved AOT values. Most substantial were differences in the Southern Hemisphere, and the cause of this was apparently insufficient reliability of cloud impact filtering. 

Many of the difficulties encountered by these early investigators were related to the insistence of the paint makers that hiding power be determined in "practical" paint systems—that is, that the amount of pigment present be based upon the amount required to produce brushing viscosity in a simple linseed oil vehicle. Since pigments varied in both density and oil absorption, pigment volume concentrations were seldom comparable. The same paint makers also insisted upon a "practical" brush application and preferred visual to instrumental comparisons. 

FIGURE 9.2 Subjective versus instrumental comparison of methods. (From Tiede, M.G., J. Am. Oil Chem. Soc., 65, 811-815, 1988. With permission.)... 

H., Parker A.E., Primm O., Pujo-Pay M., Savidge W.B., Seitzinger S., Spyres G., and Styles R. 2004. A direct instrument comparison for measurement of total dissolved nitrogen in seawater. 

Basic Instrument Specifications Used for Instrument Comparisons... 

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