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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. See also Appendix A and Appendix E