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Data Acquisition In order to carry out the observational plan outlined in the previous chapter, it will be necessary to deploy a complex and highly integrated observing system. The characteristics of this system have been discussed in some detail in previous reports. In this chapter we will comment on only those aspects of the observing system that are in need of further emphasis or clarification. 4.1 Platforms 4.1.1 The geostationary satellite is an indispensable element of the observa- tional network. Implementation of the experiment should be made con- tingent upon having at least one such satellite, in fully functioning condition, in orbit over the region of the ground-based network. A satellite with capa- bilities comparable to the proposed SMS/GOES series, including nighttime capability (as compared with the present ATS type) would greatly increase the scientific potential of the experiment. The possibility of infrared and radar sounding from a geostationary satellite should also be given serious consideration. It would be desirable to have some backup capability in the form of a second geostationary satellite that could be moved into the area of the experiment, should the first one fail. Polar-orbiting satellites with infrared sounding capability for deducing temperature will be helpful in analyzing subtropical regions. 4.1.2 The primary function of ships will be to serve as fixed platforms for radar and radiosonde observations. Vessels used for this purpose need not be 19
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fully instrumented for research purposes. The network configurations dis- cussed in the previous section will require 8-10 ships on station, continuously, throughout the 3-month period of the experiment. If oceanographic research vessels are included as part of the ship-based network, a conflict may arise between meteorological needs, which are best met by maintaining the ships in fixed positions, and oceanographic needs, which require some degree of mobility. A workable compromise can, in all probability, be worked out by allowing these ships to operate freely within some specified radius of their prescribed locations. A radius as large as 5 percent of the ship spacing (about 12 km), would not present serious diffi- culties from a meteorological point of view. 4.1.3 Aircraft will perform two functions in the experiment: (a) Dropping sondes from altitudes about, or higher than, 35,000 ft on trans-Atlantic flights. The extent of required dropsonde coverage has not yet been estab- lished. (b) Intensive sampling of the internal structure of convective en- sembles. This task will require highly instrumented aircraft capable of flying at levels from 500 ft to 55,000 ft. Measurements will include Doppler winds, aerial photography, convective-scale vertical motions, temperature, relative humidity, liquid-water content, drop size, certain radiative fluxes, vertical fluxes of moisture, and sensible heat. To obtain the needed measurements, it will be necessary to have six to ten aircraft in the air simultaneously during periods of intensive sampling (about one day in four). These will include two to four flying below cloud base (these should be equipped with inertial plat- forms), one or two near or above the cloud tops, and the remainder at inter- mediate levels. A minimum number of 10-12 well-instrumented aircraft appear to be re- quired to carry out the intensive sampling outlined in (b). We note that this is about double the number of aircraft presently committed for the experiment! 4.1.4 Tethered balloons show considerable promise as a tool for monitoring the subcloud layer. These devices should be placed on as many ships as possi- ble. To be of use in the experiment, balloons must be developed that are capable of staying aloft during periods of disturbed weather. 4.1.5 Buoys may be of some limited use for surface observations. Highest- priority meteorological observations are wind and rainfall. Hourly observa- tions would be sufficient. From a meteorological point of view, one addi- tional ship in the network would be of more value than many buoys. 20
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4.2 Radiosonde Observations Accuracy requirements are (a) Dropsondes: winds to 2 m sec"1 in about 150-mbar or layers; other parameters of less importance. (b) Ship-based network: winds to 1 m sec"1 with vertical resolution to at least 2 km; preferably 1/2 km. Temperature to 0.2°C. Mixing ratio to 0.5 g/kg. If the proposed Omega system cannot fulfill the wind requirements, serious consideration should be given to implementing the loran system over the limited region of the ship-based network. 4.3 Radar In past experiments, the processing of radar data has lagged so far behind the rest of the data processing that much of the potential of this component of the observational network has not been realized. Since we anticipate that radar will play a major role in the proposed observing system, it is extremely important that this situation be remedied in the time that remains before the experiment. There is need of a quantitative meteorological radar system with real-time, digital data processing. This would reduce vast accumulations of radar film to a manageable amount of digital data which can be integrated with the other results of the experiment. It would also facilitate displays of the dis- tribution of radar echoes over the entire ship-based network, in real time, which would be useful for planning aircraft routing. There is also need for further work in relating radar data to enhanced cloudiness images from the satellite. The latter may be extremely useful for intercalibrating the radar echoes at various distances from the receivers and from different types of equipment. The problem of deducing rainfall rates from calibrated radar and satellite information deserves immediate attention. 21