A radar system is disclosed for obtaining data to map planets employing and S-band ranging transponder (RT) that is widely separated from and in motion relative to a stationary transmitter-receiver station (STRS) on earth. The STRS transmits a ranging signal which is biphase modulated by a pseudonoise (PN) code, and the RT retransmits the PN-modulated signal on a different carrier frequency. The STRS receives the retransmitted signal as a reflected signal from an area of the planet (AP) being mapped. Three time-varying delay times (STRS to RT, RT to AP and AP to STRS) are involved in the round trip communication delay. That round trip delay and a doppler shift of the reflected signal are tracked by the STRS for mapping. That is done by recording the received signal in phase quadrature at baseband. The technique for obtaining mapping data then consists of multiplying the recorded signal by a locally generated PN code after synchronizing the PN code modulation of the signal to the local PN code, and separating the synchronized PN-code-modulated signal from the rest of the received signal by a low-pass filter. The separated PN-code-modulated signal corresponds to a narrow strip or contour line at constant range from the RT which is substantially orthogonal to virtually parallel contours of doppler shift caused by motion of the RT relative to the AP. A filter which matches the doppler shift can thus be employed to resolve individual mapping points for display.
A radar mapping technique employing a synthetic aperture radar in conjunction with a correlator for directing an object moving in mid air to a desired point on the ground, which point is determined by correlating direct and indirect return signals from the ground and through the moving object respectively.
A process for correcting data from a bistatic synthetic aperture radar to eliminate distortions and resolution limitations due to the relative positions and motions of the radar transmitter and receiver with respect to a target.
A method and apparatus for resolving Doppler frequency shift ambiguities in pulse Doppler radar systems provides a radiated signal that is modulated with a periodic waveform having a plurality of pulses within a period, the interpulse intervals between pulses in the period being unequal. Radar target returns are autocorrelated for a plurality of lags, which may include the interpulse intervals and linear combinations thereof. The calculated arguments .theta..sub.Ci of the autocorrelation function are unwrapped by adding 2k.sub..pi., k=0, .+-.1, .+-.2, . . . , to the phase .theta..sub.C1 obtained for the shortest lag T.sub.1 and determining an integer m.sub.k2 from .vertline.(.theta..sub.C2 +2m.sub.k2 .pi.)-(T.sub.2 /T.sub.1).theta..sub.C1 .vertline. <.pi. and then setting .theta..sub.2 =.theta..sub.C2 +2m.sub.k2 .pi.. Phase angles .theta..sub.3, .theta..sub.4, . . . , .theta..sub.m are unwrapped in a similar manner, the integer m.sub.ki being determined from .vertline.(.theta..sub.Ci +2m.sub.ki .pi.)-(T.sub.i /T.sub.i-1).theta. .sub.Ci .vertline.<.pi.. The unwrapped phase angles and the point (0,0) are least mean square fitted to lines of phase angle vs lag for each value of k. The root mean square error of the phase angle offset from each line is determined and the slope of the line with the minimum RMS error is chosen as the Doppler frequency shift from which the velocity of the target is extracted.
The field-of-view is line-scanned transverse to movement of a vehicle such as an aircraft and the line scan signal is transmitted to a ground station in which a frame is assembled on a line for line basis with updating by each new scanning line to obtain a running picture to be displayed and imaging passage of the vehicle over the field-of-view. Additional information may be juxtaposed and superimposed. The scanning-display path may be part of a loop linked through an operator observing the display and manipulating remote control for the vehicle.
A continuously-flowing loop of electromagnetic energy extends between Earth and an object in space. Information is both loaded into the loop and extracted therefrom. To these ends, a first transmitter may be located on Earth along with a first receiver. On the distant object, such as the Moon or a satellite, a second transmitter is located together with a second receiver. Electromagnetic radiation is directed from the first transmitter to the second receiver and from the second transmitter back to the first receiver. Information imposed on the radiation is coupled from the first receiver to the first transmitter and from the second receiver to the second transmitter. The receivers and transmitters together with the coupling means and propagation in space between Earth and the distant object establish the continuously-flowing loop of information. Included also is apparatus for entering information into the loop and apparatus for extracting information from the loop.
