User manual VAISALA SKY CONDITION ALGORITHM BROCHURE FOR VAISALA CEILOMETER CL31

[. . . ] Box 26, FIN-00421 Helsinki, FINLAND Tel: +358 9 894 91 Fax: +358 9 8949 2485 Email: metsales@vaisala. com www. vaisala. com Sky Condition Algorithm for Vaisala Ceilometer CL31 Features/Benefits · Produces sky condition information from a single ceilometer · New calculation algorithm - good results compared to human observers · Optional for the CL31 ceilometer · Generally used in automatic surface weather stations and airport weather monitoring systems The CL31 ceilometer can be configured to report sky condition automatically and accurately. The Vaisala Sky Condition algorithm is an easy and cost-effective way to produce more information from ceilometer data. The algorithm is included in the CL31 software as an option. Operation principle of the algorithm The conventional algorithms evaluate a histogram of cloud hits during the last 30 minutes. [. . . ] Basic operation of CL31 Sky Condition Algorithm. The new algorithm computes in 2D time-height domain. Reliable results with automatic measurement The new Sky Condition Algorithm has shown good results in comparison to sky condition reported by human observers (1. For comparison, success percentage values for the ASOS ceilometer algorithm (2, CT25K embedded algorithm and the new Sky Condition algorithm are presented in table 1. Picture of whole sky from one point The purpose of the algorithm is to construct an image of the whole sky based on the ceilometer measurements only from one single point. The sky condition algorithm uses a time series of ceilometer data to calculate the cloud amount of different cloud layers and the corresponding layer heights. Sky Condition algorithms are generally used in automatic surface weather stations and in airport weather monitoring systems. SKY CONDITION ALGORITHM FOR CL31 CLOUD HEIGHT Technical Data Data collection A new sky condition message is calculated every five (5) minutes based on data collected during the last 30 minutes. The last 10 minutes are double-weighted. Compatibility Vaisala Sky Condition algorithm is fully supported by CL-View Graphical User Interface for Ceilometers. Sky Condition message can be viewed either in the main window or in a separate window. CL-View provides cloud layer height and information in either text or symbol format. Data display The Sky Condition message line is included in the CL31 Ceilometer data message 2 and its subclass. The message output interval is the same as the ceilometer data acquisition interval. Message line The Sky Condition message line in data message 2 and its subclass is: 1 055 3 170 6 230 0 /// 0 /// where: 1 the first number of the line: detection status as follows: 0 . . . 8 Cloud amount of the first layer in oktas 9 Vertical visibility -1 Data missing or the ceilometer is in standby mode 99 Not enough data (after start-up) 055 The second number of the line: Height of the 1st cloud layer (5, 500 ft or 550 m depending on feet or meter selection) 3 The third number of the line: Cloud amount of the 2nd layer in oktas 170 The fourth number of the line: Height of the 2nd cloud layer (17, 000 ft or 1700 m depeding on feet or meter selection) 6 The fifth number of the line: Cloud amount of the 3rd layer in oktas 230 The sixth number of the line: Height of the 3rd cloud layer (23, 000 ft or 2300 m depeding on feet or meter selection) 0 The seventh number of the line: Cloud amount of the 4th layer in oktas /// The eighth number of the line: Height of the 4th cloud layer 0 The ninth number of the line: Cloud amount of the 5th layer in oktas /// The tenth number of the line: Height of the 5th cloud layer Table 1. [. . . ] 16th Conference on Interactive Information Processing Systems. American Meteorological Society. (2 Specifications subject to change without prior notice. [. . . ]