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Omega Sky Wave Corrections

IP.com Disclosure Number: IPCOM000082089D
Original Publication Date: 1974-Oct-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 4 page(s) / 17K

Publishing Venue

IBM

Related People

Marazas, GA: AUTHOR

Abstract

Data received by a computer from an Omega navigation aid receiver, is converted by fitting of a mathematical model against those sky-wave correction factors associated with area mapping, as prepared and published by the Defense Mapping Agency, Hydrographic Center.

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This is the abbreviated version, containing approximately 41% of the total text.

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Omega Sky Wave Corrections

Data received by a computer from an Omega navigation aid receiver, is converted by fitting of a mathematical model against those sky-wave correction factors associated with area mapping, as prepared and published by the Defense Mapping Agency, Hydrographic Center.

Omega receivers produce digital outputs which reflect geographic positions of the receiver, from radio waves propagated from fixed master stations. For each mapping area, an offline data analysis program evaluates and stores five data words, which define a model for the given sky-wave correction factor. An online program selects that stored model appropriate to the present position estimated for own ship.

The selected model is exercised, as required, to determine the sub-correction factor for each of the Omega stations then in use by the Omega receiver. These subfactors are combined in standard Omega sequence, to deliver the correction factors applied to the lines of position determined by the Omega receiver.

A maximum of 8 Omega stations are involved with 3270 models per Omega Station and 5 data words required per model. In the model, the correction factor is characterized by the following features: nighttime correction is constant, daytime correction is variable and given by the Swanson diurnal function, effective time of sunrise and sunset is calculated based upon the Swanson diurnal function, and linear interpolation is employed during times of day/night transition.

The five data words of each model have the following contents: WORD NUMBER BITS 0 to 7 BITS 8 to 15 1 N for Fall, Winter O for Fall, Winter 2 N for Spring, Summer O for Spring, Summer 3 A1 A2 4 Control Information A3 5 Sunrise Slope Sunset Slope.

The Fall, Winter period is from October 1 to March 31 and the Spring, Summer period is from April 1 to September 30. The symbol N denotes the nighttime correction factor. For given periods, N is equal to the weighted average of the maximum correction factors during each 24-hour day, for each tabulated half-month period. Note the maximum here means the negative number with largest magnitude.

The factor O is an offset factor, based upon N above the average daytime correction factor D and the empirical factor M from Swanson's model. For the given time of year, D is equal to a weighted average of the minimum correction factors during each 24-hour day, for each tabulated half-month period. Note, the minimum here means the number with smallest value, where positive numbers have less value than negative numbers. The factors N and D lead to the base- correction factors during night and day, respectively. These base factors embody the factors of ground conductivity and orientation with respect to the earth's magnetic field, as described in the Swanson Model.

The factors A1 to A3 are geometric in nature. They lay the

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foundation for modeling the effects of daytime/nighttime geometry, as given by the Swanson Model. To evaluate the A f...