24 A WORLD ATLAS OF ATMOSPHERIC RADIO REFRACTIVITY 



7.3. Accuracy of Gradient Maps 



It is very difficult to assess the probable errors 

 in the maps of the different kinds of initial 

 gradients given in appendix C. The primary 

 reason for this is that no data are available ex- 

 cept those used to prepare the maps. It is likely 

 that the most serious source of discrepancies 

 will arise because of the admixture of data taken 



at widely differing local times. In line with the 

 results of the AN error analysis, an overall 

 error of about 15 percent of the contoured val- 

 ues seems reasonable, but may be higher or 

 lower, depending on the area being considered. 

 The maps in appendix C are probably best suit- 

 ed for the depiction of climatic tendencies of 

 subrefraction and superrefraction. 



