Method of extracting phase errors caused by the atmosphere in the backscatter signal of a coherent imaging radar system carried by a carrier from radar raw data and apparatus for carrying out the method

• US 5,257,028 A
• Filed: 07/08/1992
• Issued: 10/26/1993
• Est. Priority Date: 07/19/1991
• Status: Expired due to Fees

• Current Assignee: Deutsche Telekom AG
• Original Assignee: Deutsche Telekom AG
• Inventors: Moreira Neto, Joao R., Keydel, Wolfgang
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US07/910,589
• Time in Patent Office: 475 Days
• Field of Search: 342/25, 342/26, 342/159
• US Class Current: 342/25.00D
• CPC Class Codes: G01S 13/90 using synthetic aperture techniques , e.g. synthetic aperture radar [SAR] techniques
• CPC Class Codes: G01S 13/9011 with frequency domain processing of the SAR signals in azimuth G01S13/9005 takes precedence
• CPC Class Codes: G01S 7/40 Means for monitoring or calibrating

Abstract

In a method of extracting phase errors caused by the atmosphere in the backscatter signal of an on-board coherent imaging radar system from radar raw data, firstly to image areas with different backscatter ratios over a predetermined period of time consecutive azimuth spectra are continuously formed. Thereupon, a frequency offset (ΔF(t)) of the backscatter ratio component is obtained by determining the location of the maximum of the correlations between two respective immediately consecutively formed azimuth spectra. Then, a double integration for the difference of the frequency offset (ΔF(t)) and a desired value (ΔF_soll) of the frequency offset is carried out, the frequency offset desired value (ΔF_soll) being determined either from the carrier forward velocity (V_v) or by a low-pass filtering of the frequency offset (ΔF(t)), and finally for standardization the result of the double integration is multiplied by a constant (2π/Δt) to obtain thereby the phase error (φ_e (t)).

Claims

1. A method of extracting phase errors caused by the atmosphere in the backscatter signal of a coherent imaging radar system carried by a carrier from radar raw data in which

for imaging areas with different backscatter ratios over a predetermined period of time successive azimuth spectra are continuously formed and

a frequency offset (Δ

F(t)) of the backscatter ratio component is obtained by determining the position of the maximum of the correlations between two respective immediately successively formed azimuth spectra,

wherein;

performing a double integration of the difference of the frequency offset (Δ

F(t)) and a desired value (Δ

F_soll) of the frequency offset, the frequency offset desired value (Δ

F_soll) being determined either from the carrier forward velocity (V_v) or by a low-pass filtering of the frequency offset (Δ

F(t)), and

standardizing a result of the double integration by multiplying said result with a constant of (2π

/Δ

t) to obtain the phase error (φ

_e (t)).

2. An apparatus for extracting phase errors caused by the atmosphere in the backscatter signal of a coherent imaging radar system carried by a carrier from radar raw data comprising:

means for detecting an azimuth spectrum to form continuously successive azimuth spectra,

means for correlation formation between two respective directly successively formed azimuth spectra and

means for forming the maximum of the correlation and determining the frequency offset (Δ

F(t));

means for forming a difference from the frequency offset (Δ

F(t)) and a desired value (Δ

F_soll) of the frequency offset, the desired frequency offset (Δ

F_soll) being determinable from the carrier forward velocity (V_v) or by a filtering of the frequency offset (Δ

F(t)) by means of a low-pass filter;

two integrating units connected in series and following said difference-forming means; and

a standardizing unit which follows the second integrating unit and at the output of which the phase error (φ

_e (t)) caused by the atmosphere is obtained.