===== UM =====
==== Umkehr Observations ====
 
UM results in data being collected which can be processed to produce an Ozone vs. Height profile. Data is normally collected between solar zenith angles of 60 ° and 90° in the morning and in the afternoon. 

The zenith prism is pointed to a solar zenith angle of 0°, FW#1 is set to the 0 position, FW#2  is set to the 0 position, the iris is opened, and the Tracker is rotated CCW until it is perpendicular to the sun. Intensity measurements are made at two sets of wavelengths - long (320-330nm) and short (310-320nm), and continue until they are interrupted by the operator, or by the next zenith angle in a schedule. 

Raw data is put into the BJJJYY.nnn file, and is processed to a UJJJYY.nnn file by the SUM command.