Patent GB-797271-A (GB)
Title: Method of and apparatus for determining or forecasting the future value of certain meteorological parameters
IPC: G06G7/26
Filed: 1954-06-08
Abstract: 797,271. Electric analogue calculating systems. GIAO, A., and RAYMOND, F. H. June 8, 1954 [June 12, 1953], No. 16843/54. Addition to 749,589. Class 37. General.-In apparatus for determining or forecasting the future value, at a given geographical point after a given time interval from a datum, of a meteorological parameter p such as atmospheric pressure, wind velocity, temperature or the like, defined by its satisfying equation (1) set forth in the parent Specification, from a chart of mean isothermal lines, a chart of isolines indicating the initial condition of the function Fo of the unknown parameter as defined by equation (6) of said Specification, and a chart of iso-curves of a factor # defined below, there are provided :- (a) Means for automatically scanning the chart of mean isothermal lines along meridians commencing with a datum meridian containing or lying closely adjacent to the given point and proceeding along successive meridians lying in an upstream direction (i.e. contrary to the direction of transfer movement of Fo) from the datum meridian, until an area has been scanned proportional to the given time interval after allowance for corrections necessitated by variations of the chart scale along the meridians; such area lying between a pair of isothermal lines of which one intersects or passes adjacently to the given point, the datum meridian, and a further meridian displaced therefrom in an upstream direction; (b) Means for scanning the isoline chart along meridians commencing with a datum meridian containing or passing adjacently to the given point and proceeding similarly along successive meridians in an upstream direction from datum; (c) Electrical means for counting algebraically the isolines traversed by each scanning line of the isolinear chart to determine at each time instant of the count the value of the function Fo for the position attained by the scanning means and to obtain a voltage representing the value of Fo at a point on the said meridian and lying either on or between the said pair of isothermal lines; this value representing the value [Fo] of the function Fo to be transferred to the datum meridian during said time interval; (d) Means for scanning the chart of # isocurves along meridians commencing from a datum meridian containing or lying adjacent to the given point and proceeding along successive meridians in an upstream. direction from datum ; (e) Electrical means for counting algebraically the # isocurves along each scanning line of the chart thereof to determine at each instant of the count the value of po for the position attained by the scanning means, and deriving therefrom a voltage representing # at a point on said further meridian and lying either on or between the said pair of isothermal lines; (f) Electrical means for multiplying the said value of # by the said value [Fo] of Fo ; (g) Electrical means for multiplying the value [#Fo] by weight function defined by equation (5) of said Specification to produce a representative product voltage; (h) Means for initiating repetitive performance of the operations set forth above with respect to further pairs of isothermal lines displaced towards the geographical pole from the first pair of isothermal lines; and (i) Means for electrically integrating the succession of representative voltage product values of #[Fo] multiplied by the weight function while eliminating therefrom the factor #. Theory.-In the Specification 749,589 referred to, the variable function p(t) was treated as an analytic function having finite derivatives of any order, but in the present apparatus this may be a generalised non-analytic function, and there is introduced into the function Fo of the unknown parameter # (e.g. pressure) a factor # defined by : where a, b, k, c are constants ##o=the initial value of parameter p+a constant necessary to give positive values. #o=the value of # for #=0 6= transfer time along the isotherms. E #fn is the sum of the frontal discontinuities of # along the transfer isotherm from the origin of integration. An additional scanned chart of isocurves of the factor # is therefore utilized in conjunction with the scanned charts of mean isotherms and isolines of the initial condition of the function Fo of the unknown parameter to be determined, referred to the same portion of the Earth's surface on Mercator projection. In a first operation (Fig. 1, not shown), the values of the function Fo of the forecast para- A meter po given in equation (6) of the Specification referred to and transformed into are computed, multiplied by factor #, and transferred along the streamlines (which are isotherms of Tm) of the transfer velocity vector #H. A general solution for #p is given by at a geographical point A defined by co-ordinates #, # so that referring to the Figures of the above Specification and considering the streamlines of H traversing the meridian of A, there must be calculated points B of the streamlines H which are spaced from the meridian by a transfer time t given by where # is the angular velocity of terrestrial rotation r = mean terrestrial radius. R = the gas constant for air. E = the Mercator scale of the field represented. #Tm = the constant difference of Tm in degrees Centigrade between successive isotherms. #N<SP>1</SP> = the distance in millimetres between successive isotherms. Function Fo is determined at these points, and its values multiplied by # are plotted on the meridian of A on the corresponding streamlines. In a second operation, the future values of the parameter, e.g. the pressure at point A(#0, #) are determined by computing the integral, along the meridian of A from #0 to #/2 of the transferred function [pFo], introducing the constant 1/# and the function G(#, #0). The first element of the apparatus must therefore calculate the expression where [#Fo] is a function of (#, #, t) resulting from the transfer of [#Fo] by vector H (#, y) in which the weight function G(#, #o) is continuously derived for variable values of #when #0 is fixed, by selecting the geographical point point A(#0, #) at which the forecast is to be made. Since where k is a constant, the value of the function G is independent of time and expressible as (7) 1/h G=G<SP>1</SP>(α,#o)=tan # (cos α-tan #o sin α) wherein α=# - #0 and equation (5) is calculable in terms of a as in response to the analogue voltage of the variable α; this variable being represented by a signal derived from a potentiometrically controlled resistance-capacitance circuit as a function of t in the form α=Á t/ac; the constant Á, being introduced by adjustment of the potentiometer slider; the signal α being applicable to a servo-system driving a number of potentiometers in response thereto for multiplication by α in the forecast computation. A set of six discrete values of [#F0] for the respective different streamlines of H are derived, and representing these discrete values by [#F0]j at different latitudinal values #j, it is shown that by interpolation, where j may be any integer from 1 to 6, The several distinct values of [#Fo] j  are automatically registered in succession in the computer as set forth below, which carries out the necessary multiplications by G<SP>1</SP>[#Fo]j j+1 , G<SP>1</SP>[#Fo] j , 1/αj+ 1 αj,αj, and α as necessary; the terms being subsequently regrouped after multiplication to obtain the function of α to be integrated, Œ a constant. In the integration, it is necessary to employ switching to (a) arrest the integrator when α attains the value α+j 1 ; (b) arrest the integrator delivering I(#0) when α attains the value α j+1 ; (c) advance the sequence switching by one step to substitute index j=1 for index j at prescribed intervals. Structure and operation.-In Fig. 2, the isotherms of Tm incribed on a transparent plate 301 are scanned according to a vertical scanning lav for Mercator's projection, by a cathode-ray tube spot, and from equation (4) above the transfer time t due to the velocity field #H(#, #) is given by it being shown that the vertical scanning voltage function for Mercator projection is given by where # is the time of traversal of the spot over adjacent isotherms. Voltage pulses for each intersection are generated by photocell 302 receiving the emergent light and are fed into a selector 361 for the appropriate isotherm, followed by an integrator 338 summing the elementary transfer times # #d#, multiplied by the appropriate coefficients, and fed to a comparator circuit 340 into which is set a manually adjustable voltage representing a given forecast time interval TR. At equality denoting expiry of this time, a pulse signal is transmitted to control line selector 361, isoline counter 331b, isocurve counter 331a, isoline interval counter 331c, and computor 312 for function [ #Fo] ; thus starting the computation of [Fo] at a point of the isothermal chart at which co-ordinates (#), A) correspond to a transfer time of TR on the isotherm intersecting (#j, #a) so that the value of the transferred function [Fo] on meridian #+#a is obtained, by scanning the isolines of log po inscribed on transparent plate 303. These are scanned by a cathode-ray spot along successive parallel meridians synchronously with the scanning spot of the Tm isothermal chart, to produce voltage pulses at photocell 304, which are algebraically counted in binary isoline counter 331b controlled by the forecast time expiration pulse to produce signals which represent at any time the total value of the A isolines of log p at the point then reached by the scanning spot. Isoline interval binary counter 331c is responsive to a train of fixed frequency pulses generated over a time interval determined by the pulses generated by the scanning intersection of adjacent isolines, subject to overriding control by the forecast time expiration pulses to