DETERMINATION OF ICE THICKNESS

• US 3,665,466 A
• Filed: 03/20/1970
• Issued: 05/23/1972
• Est. Priority Date: 03/20/1970
• Status: Expired due to Term

• Current Assignee: Haines C. Hibbard
• Original Assignee: Haines C. Hibbard
• Inventors: Hibbard, Haines C.
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US05/021,325
• Time in Patent Office: 795 Days
• Field of Search: 343/5R,12R,13R,14 324/4,5,6
• US Class Current: 342/59
• CPC Class Codes: G01B 15/02 for measuring thickness
• CPC Class Codes: G01N 22/00 Investigating or analysing materials by the use of microwaves or radio waves, i.e. electromagnetic waves with a wavelength of one millimetre or more G01N3/00 - G01N17/00, G01N24/00 take precedence
• CPC Class Codes: G01S 13/345 using triangular modulation

Abstract

The thickness of sea ice is measured using a radar technique with radio frequency energy having frequency in the range between a frequency below 2000 MHZ and a frequency above 4000 MHZ. The penetration of radio frequency energy transmitted from above the ice and reflected by the ice or the water below it depends on the frequency of the energy. The frequency may be swept over the above range and the travel time of reflected energy recorded to obtain a measure of the salt concentration in ice.

Claims

1. A method of measuring the thickness of sea ice comprising:

from above the ice, irradiating the upper surface of the ice with radio frequency electromagnetic waves of frequency above 4000 MHz and measuring the two-way travel time of waves reflected by the upper ice surface, and irradiating the upper surface of the ice with radio frequency electromagnetic waves of frequency below 2000 MHz and measuring the two-way travel time of waves reflected at or near the lower ice surface; and

utilizing the difference in travel time thus measured and the velocity of radio frequency waves in ice to obtain the ice thickness.

2. The method of claim 1 wherein the frequency of the radio frequency waves is repetitively varied between a frequency less than 2000 MHz and a frequency above 4000 MHz.

3. The method of claim 2 wherein a record is made of two-way travel time for each of a plurality of frequencies between said frequency below 2000 MHZ and said frequency above 4000 MHZ.

4. The method of claim 2 wherein the frequency of the radio frequency waves is continuously varied in frequency.

5. In the measurement of the thickness of ice covering a body of water using radio frequEncy waves, the improved method of determining the travel time of radio frequency waves through the ice comprising:

from a location above the ice, irradiating a portion of the upper surface of the ice with radio frequency waves at each of a multiplicity of frequencies between a frequency less than 2000 MHz and a frequency above 4000 MHz;

producing a first electrical signal having an amplitude indicative of twoway travel time of waves reflected by the ice or the body of water for each of said multiplicity of frequencies;

producing a second electrical signal indicative of the rate of change of said first electrical signal;

the duration of said second signal above a given amplitude being indicative of the two-way travel time of said radio frequency waves through the ice, and the magnitude of the signal being indicative of the rate of change of salt content of the ice.

6. The method of claim 5 wherein the upper surface of the ice is irradiated with radio frequency waves continuously variable in frequency between said first and second frequencies.