AN/GMQ-13 CLOUD HEIGHT SET

Operation Figure 2-39.—RO-546/GMQ-13 GIFFT cloud height recorder. conjunction with the ML-121 ceiling light projector. Ceiling balloons may also be used to determine cloud height, both ashore and at sea. AN/GMQ-13 CLOUD HEIGHT SET The AN/GMQ-13 cloud height set was introduced to the fleet from 1955 to 1959. Over the years many modifications have been made to the individual pieces of equipment. Currently, the cloud height set consists of an ML-506/GMQ-13 rotating beam projector, an ML- 507/GMQ-13 cloud height detector, and an RO- 546/GMQ-13 GIFFT ceiling height recorder. The projector and the detector are permanently installed near the main runway, but are separated by a 400- to 900-foot baseline. See figure 2-38 for a standard setup diagram. The standard baseline is 400 feet. Cloud height is determined by the angle of the projected light beam reflected from the base of the clouds directly overhead the receiver. The GIFFT cloud height recorder, usually rack-mounted in the observer’s space (fig. 2-39), records angle-of-reflection on a chart. Detailed information on the theory of operation, operating instructions, and maintenance guidance for the projector and receiver is contained in NA 50- 30GMQ13-1, Handbook, Operation and Service Instructions, with Illustrated Parts Breakdown, Cloud Height Set AN/GMQ-13(C). Operation and maintenance guidance for the RO-546/GMQ-13 GIFFT recorder is published in the manufacturer’s instructions provided with the equipment. Evaluation of the Recorder Trace The RO-546 recorder chart is marked in hours and tens of minutes. The time marking "234" equates to 2340Z. Time adjustments are covered in the operator’s manual. The procedure used to determine cloud height using the GIFFT recorder has been refined since the manufacturer provided the operator’s manual. The recorder elevation angle is evaluated differently for various weather conditions. In some cases, the indicated elevation angle must be corrected to obtain an accurate cloud-base height. CORRECTION FACTOR.—An equipment correction must be determined for each individual GIFFT recorder before any recorded elevation angles may be used to determine cloud height. The following procedure is used for RO-546 recorders when the ML- 506 RBC projector and ML-507 RBC receiver are separated by the standard, 400-foot, baseline. To obtain the equipment correction, make a recording of a high, solid cloud cover with bases between 10,000 and 20,000 feet. This solid cloud cover should produce a fairly consistent solid band, 4° to 8° wide, on the recorder chart. Solid, well-defined cloud bases will produce a shorter trace, while diffuse or ragged bases will produce a longer trace. See figure 2-40. The occasional horizontal lines marked outside Figure 2-40.—Determining equipment correction from high, solid cloud cover. 2-31