• 专利附录
  • 专利说明
  • 权利要求
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    • 专利摘要:
    The invention describes a device and method for determining the local geomagnetic disturbance at medium latitudes by eliminating the different components of undisturbed geomagnetic field, which solves the problems existing in the known state of the art. For this purpose, in the present invention a day model in geomagnetic calm at medium latitudes is described for the horizontal component (h) of the geomagnetic field. The procedure involves the characterization of day in calm or disturbed day by an assessment of the goodness of fit of the invented model to the measured data of the horizontal component of local magnetic field, once subtracted an auxiliary trend curve of the night values. The procedure can be implemented in the device to determine the local geomagnetic disturbance in real time. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2640934A1
    申请号:ES201600258
    申请日:2016-04-05
    公开日:2017-11-07
    发明作者:Antonio GUERRERO ORTEGA；Consuelo CID TORTUERO；María Elena SAIZ VILLANUEVA；Judith PALACIOS HERNÁNDEZ；Yolanda CERRATO MONTALBÁN
    申请人:Universidad de Alcala de Henares UAH；
    IPC主号:
    专利说明:

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    • 214: search stage of the geomagnetic calm day closest to the current one in database 225, which is executed after a negative response in 213;
    • 225: database of calm geomagnetic days saved after positive responses in 213;
    • 226: baseline calculation stage;
    • 31 (continuous line): curve of the data to be adjusted by the calm day model, calculated from the horizontal magnetic field component and once the auxiliary trend curve of the night values has been subtracted;
    • 32 (dashed dashed plot): daily variation curve obtained from the adjustment of the calm day model;
    • 331-334: control points of the cubic spline, of type (N), fixed in temporal (horizontal) and intensity (vertical) position, of the calm day model;
    • 341-344: control points of the cubic spline, type (P), fixed in temporary position but free in intensity, of the calm day model;
    • 40: device for obtaining local geomagnetic disturbance;
    • 41: data input unit of device 40;
    • 42: CPU of device 40;
    • 43: device data storage unit 40;
    • 44: device data output unit 40. Description of an embodiment of the invention
    As is known, the measurement of the magnetic field on the earth's surface has different contributions that, in certain situations, can be identified as three distinct components:
    I) an internal component, composed of the main component, whose origin is in the dynamo process that takes place inside the Earth and a component due to the earth's crust and mantle;
    II) a component of "Calm Sun", originated by the equivalent system of ionospheric currents of diurnal nature;
    III) a component of disturbance, due to sources external to the terrestrial environment, such as that which occurs irregularly and sporadically due to solar activity.
    The present invention deals with the determination of the first two components I), II) to obtain the local geomagnetic disturbance generated by solar activity, component III), in order to be able to predict potentially dangerous situations such as those listed in the heading Technical problem to solve.
    Overview of the procedure
    To give a global vision and a better understanding of the procedure, figures 1 and 2 have been made showing the curves involved in the procedure and a flow chart thereof, respectively.
    The evolution of the horizontal component of the measured local geomagnetic field, curve (11), together with the different curves involved in the procedure, (12) - (14) has been represented in the upper panel (1a). In the lower panel (1b) the result of applying the procedure described in the present invention, curve (15) has been represented. In the case of figure 1a, the measured data, represented by (11), have been provided by the geomagnetic observatory of San Pablo de los Montes in Toledo, Spain, identified internationally with the acronym SPT (code given by the IAGA body, International Association of Geomagnetism and Aeronomy). The number in parentheses in the title of the ordinate axis corresponds to the value (expressed in nanoteslas, nT) that must be added to the values offered in the ordinate axis to obtain the absolute value of the measure. The time at which the measurement is made, given in magnetic local time (MLT), is represented on the lower abscissa axis. The upper abscissa axis represents time expressed in universal time (UT). The difference of 16 minutes that can be seen between both time scales corresponds to the time difference equivalent to the difference between the geographic reference length of the Greenwich meridian and the length of the SPT observatory where the measurement is made. The time window of Figure 1 has a duration of five days.
    The flowchart of the entire procedure is shown in Figure 2. As can be seen there is an initial block (20), two vertically oriented main blocks or sub-procedures (21) and (22), and a final block (23). The main blocks carry out the determination of component II) in block (21) and the determination of component I) in block (22). The final block (23) is nothing more than a subtraction of components I) and II), results of (21) and (22), to component H of the measured data.
    The first block (20) is a preprocessing of the measured data where, among other operations, an association of the values to its temporal reference in the local magnetic system MLT is performed. For this, it is necessary that the measurement of the geomagnetic field be accompanied by some time reference in which the measurement is made, such as universal time (UT). To carry out the MLT time conversion, it is necessary to provide the position in length of the place where the measurement was made. Also, the preprocessing includes the transformation of the coordinate system, if necessary, from the field components provided by the measurement system to a format from which it is possible to extract the horizontal component (H).
    The evolution of the measured local geomagnetic field, given by the curve (11) of Figure 1, supposes the superposition of the three components: I), II) and III) previously mentioned. To obtain what this value corresponds to the geomagnetic disturbance component (component III), measured locally at a specific point in the geography, and due to external sources, that is, as a result of sporadic solar activity, it is necessary to eliminate components I) and II) described above. In figure 1a) three other curves are also represented: (12) is the auxiliary trend curve of night values, used in block (211); (13) is the daily variation curve (component II)), and (14) is the representative baseline of component I).
    The technique used in the present invention determines in the first instance the component II) for being the one that has variation (of considerable magnitude) of shorter period of time (one day), compared to periods of the order of months or greater of the component I ).
    In addition, the correct determination of component II) for a prolonged set of days in time, allows to obtain component I). Although component I) has slow variations, its behavior is difficult to predict. There are geomagnetic models, such as the IGRF model, which provide these components for past, present, and projected values in some years into the future (no more than five), but their accuracy, both spatial and temporal, is usually not sufficient for Many applications In addition, these models are obtained from processes in which the aforementioned external disturbance component (the component III) mentioned above has been previously eliminated through a global interpretation of it, for example, by using non-local geomagnetic disturbance indicator indexes but global as are the Dst index or the Kp index. Therefore, when the purpose is to obtain the local geomagnetic disturbance with precision, as in the present invention, it is not suitable to make use of said geomagnetic models. As a consequence, in the present invention, component I) is obtained from the data observed at the same location where the measurement is performed. This characteristic can be better appreciated by observing the flowchart of Figure 2: component I, obtained in block (22), is obtained from the original measured data (20), but not directly, but after making a part of the processing for obtaining component II in block (21). This way of proceeding brings to the invention two important characteristics, on the one hand, absolute independence of the procedure on external data, and on the other hand greater precision for obtaining the components for the specific location of the measure, since data is not dependent on global derivatives as would be the case with the use of geomagnetic indexes or models.
    Calm day model
    The component II) of daily variation is determined by a calm day model (relative to the horizontal component of the geomagnetic field) valid for a magnetic latitude close to that of the location of the ionospheric current system focus (approximately between 35º and 45 ° from the equator in both hemispheres), of the present invention. The model is characterized by being defined by a cubic spline, that is, a differentiable curve defined in sections by cubic polynomials (third degree polynomials). The control points are the place of union of the sections and the place where certain conditions are imposed that make the transition occur smoothly. For a cubic spline, these conditions are three and must be met at each control point. These three conditions imply continuity of the functions at the control points, and they mean that both the evaluation of the polynomial at the control point, as well as its first derivative and its second derivative must be the same for the two existing polynomials at each control point side.
    The calm day model for this embodiment of the present invention is composed of eight control points distributed over time over a day, 24 hours, fixedly at certain times of the day, as shown in figure 3, represented by rhombuses and asterisks, differentiating two types, parametric (P) and neutral (N), respectively. Figure 3 shows these points in an example of a geomagnetic calm day; to the data shown as element (31), the daily variation model has been adjusted, obtaining the curve (32). The data shown in (31) is not the original measured data, the result of block (20), but an auxiliary curve has previously been subtracted in step (211) as described in the following section. The four points (N) correspond to two points in the first four hours of the day and another two points in the last four hours of the day, that is, occupying the local night hours (hence its name with the letter N). These points (N) are characterized by being located at a magnetic field intensity set at a value of zero with respect to the base value of the calm day model. The remaining four control points, points (P), are located in the central zone, corresponding to the daytime hours of the place and have the characteristic of having a variable intensity, each offering a free parameter to the model that allows the adjustment of the data to it. In addition, the condition that the first derivative is null is imposed at the two points (N) of the ends (those corresponding to 0 h and 24 h). The model defined in this way has four degrees of freedom, due to the four free parameters (P) of the central zone during daylight hours.
    Determination of the auxiliary trend curve of night values
    Since it is based on observational data measured on the earth's surface (which, as described above, are the result of the superposition of four components), in order to make an adjustment of the calm day model, in order to obtain the component II), the data to which it conforms must contain the minimum contribution of the other two remaining components; I) and III). The technique adopted in the invention involves first determining an approximation of the two overlapping components I) and III), which are subtracted from the original data in an auxiliary manner, and which allows an adjustment of the calm day model only to the values of daily variation that best represent component II). This approximation curve, which has been called the trend curve of the night values (element (12) in figure 1b), is a smooth interpolation curve between a single daily point obtained from the average value of the hours of night, described in detail below.
    To understand the importance and in turn the validity of the determination of the auxiliary curve, the possible behavior of the other two components must be taken into account. Component I), as already said, has slow variations compared to daily variation and, therefore, an evaluation of the type that is proposed with a single daily point (representing the average value of the night zone), is more than enough to ensure its correct description. The external disturbance component III) contemplates geomagnetic variations of a very diverse nature, which for the purposes of the present invention we can differentiate into two types: III-A) major intensity variations that disturb the magnetic field irregularly and sporadically, hardly predictable and that prevent a correct determination of component II) of daily variation; and III-B) smooth but maintained variations, lasting more than one day and that may be present on a day of geomagnetic calm, due to disturbances in the previous days. Variations of type III-A) have rapid and important changes that will result in an adjustment of the invalid calm day model, and therefore, although a determination of the same is not possible, if its presence can be verified by means of measure of goodness of fit, as will be seen later. Variation III-B) translates into a gentle increase, or decrease, in the daily level of the measured geomagnetic field, and therefore the evaluation using a curve obtained by a daily point also ensures its correct determination prior to adjustment.
    At this point it should be clarified that determining, prior to the adjustment of the calm day model, the trend curve (12) as an approximation of components I) and III-B), does not mean that such variation is permanently eliminated from the original observational data, because as will be seen later, it is only used as an auxiliary curve to determine the daily variation component. In order to clarify the terminology used, it will be differentiated between elimination, a term with which we want to point out that it is the definitive subtraction operation of a contribution and with which an intermediate or final result is obtained; and the term subtraction, which indicates that the arithmetic subtraction operation is done, but only as an intermediate process that does not imply the definitive deletion of the original data.
    The auxiliary trend curve of the night values (12) is obtained from the average value reached in a set of night hours that is chosen beforehand within a symmetrical range (maximum 4 hours) of hours before and after the Local midnight transit between one day and the next. In the case of the five-day example shown in Figure 1b), the average values for the six hours of night are represented by asterisks, the area of the night hours used, from -3h to + 3h compared to midnight local, are marked with oblique stripes background. The smooth curve that passes through these mean values at night has been performed by a cubic spline, although other similar methods of interpolation by soft curve could be used. Once the trend curve of the night values is determined, it is subtracted from the measured data and the calm day model is adjusted on the result of the subtraction.
    Qualification and storage of calm geomagnetic days
    The adjustment of the calm day model to the data can be performed by minimizing a function such as that of the mean square error and evaluating the goodness of the adjustment by means of the chi-square. The melado used is an iterative process in which initial values are established for the four parameters of the same and the goodness of the adjustment is evaluated. In the process, the parameters are modified towards the value that minimizes the error function, so that they must converge towards a stable value provided that the data have a typical daily variation of calm geomagnetic day. The iterative method can be terminated by a number of iterations (if it does not converge) or by setting a threshold in the relative increase in the value of the goodness of fit between one iteration and the next, so that for increments below the threshold, ensure that the convergence process has been completed.
    The final value of the goodness of fit (chi-square value) is used in this stage (213), see figure 2, to discriminate between calm days from those that are not. If the value is high enough, it indicates that the adjustment is not good, probably because the data has geomagnetic disturbance and, therefore, cannot be considered as a calm day. The curve thus determined should not be used as component II). On the other hand, the result with a small chi-square value confirms that the curve resulting from the adjustment is a valid calm day curve and, therefore, should not only be eliminated as component II), but must be stored in a database (step (225) in figure 2) which will allow to determine component I).
    To perform this discrimination properly, a threshold value is established for the goodness of the adjustment, which can be determined in several ways depending on the amount of previous known data. If historical data are available continuously for several years, it is possible to conduct a study of the probability distribution of the chi-square values obtained for the model adjustments to each day and establish the threshold at a sufficiently high value to ensure a near zero probability of finding a calm day for values above that threshold. If historical data are not held continuously but a period of several days is available, a comparative study of the value of goodness of fit between calm and disturbed days can be carried out to establish the threshold.
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    权利要求:
    Claims (1)
    [1]
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    引用文献:
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    CN103115624B|2013-01-24|2014-12-10|南京航空航天大学|Terrestrial magnetism diurnal variation correction method based on terrestrial magnetism matching|
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