An apparatus for remotely measuring and accessing water status relative to snow and glacial melt, surface runoff, rainfall, evaporation, flow rate, and soil moisture is described. A radar target located at a selected location on the surface of the Earth is designed to collect water and render its cross sectional area variable as a function of the height of the water level within the target. The target is remotely monitored by an orbiting or airborne synthetic aperature radar. The target appears as a bright spot embedded within the radar image. The target brightness is indicative of the height of the water level within the ground located target

Sivertson, W. E., Jr.

English

NASA Technical Reports Server

a 
United States Patent [I91 
Silvertsan Jr. 
[54] RADAR TARGET FOR REMOTELY SENSING 
HYDROLOGICAL PHENOMENA 
[75] Inventor: Wilford E. Sivertson Jr., Yorktown, 
Va. 
[73] Assignee: The United State-s of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 945,041 - 
[22] Filed: Sep. 22, 1978 
[51] Int. Cl.2 ......................... GO1S 9/60; HOlQ 15/00 
[52] U.S. c1. ............................... 343/5 CM; 343/5 W; 
343/18 B: 343/18 D 
[58] Field of Search ............... 343/5 CM, 18 B, 18 C, 
343/18 D 
r111 4,184,155 
[45] Jan. 15, 1980 
References Cited 
U.S. PATENT DOCUMENTS 
3,879,731 4/1975 Mack .................................. 343/18 B 
[561 
Primary Examiner-T. H. Tubbesing 
Atforney, Agent, or Firm-William H. King; John R. 
Manning; Howard J. &born 
1571 ABSTRACT 
Apparatus for remotely measuring and accessing water 
status relative to snow and glacial melt, surface runoff, 
rainfall, evaporation, flow rate, and soil moisture. A 
radar target located at a selected location on the surface 
of the earth is designed to collect water and render its 
cross-sectional area variable as a function of the height 
of the water level within the target. The target is re- 
motely monitored by an orbiting or airborne synthetic 
aperature radar. The target appears as a bright spot 
embedded within the radar image. The target brightness 
is indicative of the height of the water level within the 
ground located target. 
11 Claims, 5 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19800010224 2020-03-21T02:27:27+00:00Z
U.S. Patent ~ m .  15,1980 Sheet 1 o f2  4,184,155 
FIG. 1 
13 
FIG. 3 
FIG. 4 
US. Patent ~ m .  15,1980 Sheet 2 of 2 4,184,155 
22 
FIG. 2 
15 
/ 
/ I-) -c. 
FIG. 5 
4,184,155 
1 
RADAR TARGET FOR REMOTELY SENSING 
HYDROLOGICAL PHENOMENA 
ORIGIN OF THE INVENTION 
The invention described herein was made by an em- 
ployee of the United States Government and may be 
manufactured and used by or for the Government for 
governmental purposes without the payment of any 
rovalties thereon or therefor. 
and the water level rises therein the target radar cross- 
section decreases. Consequently, the brightness of the 
image taken by a radar from a satellite or an airplane 
decreases as the level of the water increases. Hence, by 
5 locating many of these radar targets at selected points 
on the surface of the earth an airplane or satellite Can 
remotely monitor the different radar targets and deter- 
mine the level of the water in each of the different tar- 
gets. The level of water in a radar target is indicative of 
lo the water status at the location of that Darticular radar 
target. A radar target can have holes & the bottom of 
the catch basin thereby allowing the water in the catch BACKGROUND OF THE INVENTION 
This invention relates generally to the measurement basin to seep into the soil giving an indication of the 
of water levels and more Specifically COmxrnS aPPwa- amount of moisture in the soil by the successive time 
tus for remotely measuring at many different selected l5 measurements of water level witfin the target. 
locations on the surface of the earth the Water Status at Either one or two of the radar targee can be located 
those locations. at a selected location. The second target when used 
individual instrument for each measurement type and circular plate and an constant 
require active instruments which include power 20 image brightness. That is, the target does not collect 
water and the image brightness does not vary with supplies, recorders, transmitters and other in situ instru- 
water status. The water status is indicated by the ratio mentation. Measurement activation or recording re- quires special interrogation and, in most instances, of the brightness of the radar targets (one with water manned attendance. 
have many disadvantages. They require several differ- BRIEF DESCRIPTION OF THE DRAWINGS 
ent instruments to obtain measurements, they are not 
suitable for global, day-night, &weather measurement FIG. 1 is a cross-sectional view of a preferred em- 
systems, they are clostly and require expensive upkeep bodiment Of the invention; 
and calibration, they require complex equipment and 30 FIG. 2 is a schematic drawing showing how informa- 
high technical skills for utilization, and they do not tion is gathered from the embodiment of the invention 
provide daily multiple measurement data without con- shown in FIG. 1; 
siderable difficulty. FIG. 3 is an embodiment of the invention which 
It is therefore the primary object of this invention to includes water seepage holes in the bottom of the em- 
provide simple, inexpensive apparatus for obtaining 35 bodiment of the invention shown in FIG. 1; 
measurements of water status at many selected locations FIG. 4 is a second target that can be used with the 
on the surface of the earth. embodiment of the invention shown in FIG. 1; and 
Another object of this invention is to provide appara- FIG. 5 is a schematic drawing showing how informa- 
tus for obtaining measurements of water Status at Se- tion is gathered from the embodiment of the invention 
lected locations on the surface Of the earth in which the 40 shown in FIG. 1 combined with a second target shown 
apparatus located at each of the selected locations is in FIG. 4. 
passive. 
A further object of this invention is to provide appa- 
ratus for remotely measuring at several selected loca- 
tions on the surface of the earth the water status at those 45 
locations in which very little maintenance is required at 
the several selected locations. 
Other objects and advantages of this invention will 
become apparent hereinafter in the specification and 
drawings. 
SUMMARY OF THE INVENTION 
Prior techniques for monitoring water status use an consists of only the right circular cylinder and the flat 
The techniques for monitoring water status 25 collection; one without water collection). 
DETAILED DESCRIPTION O F  THE 
INVENTION 
Turning now to the embodiment of the invention 
selected for illustration in the drawings, the basic radar 
target shown in FIG. 1 is a complex RF body formed 
from an electrically conductive, right circular cylinder 
11 and an electrically conductive, circular flat base 
50 plate 12. Cylinder 11 and base plate 12 are connected 
and made out of materials that reflect radar signals such 
as for example, aluminum, copper or stainless steel. Base The invention is a radar target whose radar cross-sec- 
within the target. me target consists essentially of a 55 ration with the cylinder 11 mounted normal to the plate 
fight circular cylinder with its central =is perpendicu- at its center. This assembly is permanently installed 
lar to the ground level; a flat circular plate symmetri- within a formed, concrete waterproof catch basin 13. 
cally attached to the lower end of the cylinder and Internal Periphery basin wall l4 is Sloped away from 
parallel to the ground level surface; and a catch basin reflector cylinder 11 to allow an unobstructed R F  field 
including said circular cylinder and said circular plate 60 of view for a radar operated at a 45 degree depression 
for catching and retaining water. The circular cylinder angle. The intensity of this target in a radar image is a 
and the flat circular plate are made from a material function of the radar cross-section of the reflector. 
(electrical conductor) that reflects radar signals such as Also, in this configuration as water collects and evapo- 
aluminum, copper, and stainless steel; and the remainder rates in the catch basin the water surface moves up and 
of the catch basin is made from a durable material such 65 down the cylinder length. This movement modifies the 
as concrete or fiberglass. Without any water in the RF dimensions of the complex body reflector so that 
catch basin the radar cross-section of the radar target is the radar cross-section varies as a function of collected 
a maximum. As the water is caught by the catch basin water volume. 
tion varies as a function of the height of the water level Plate l2 a ground plane and base for the cOnfigu- 
3 
4,184,155 
4 
The radar cross-section for the configuration in FIG. scans across the two images and by an electronic di- 
vider connected to the scanning means to produce the 
ratio of the intensities of the two images. 
By modifying the catch basin configuration, water 
5 flow and soil moisture can be measured. Flow can be 
measured by locating the modified target in a bamed 
flume. The modified target is designed so the catch 
basin has two opposing sides that are open to water flow 
and a relative size restriction is placed in the exit open- 
lo ing. This design will allow water level around the cylin- 
der to vary as a function of flow rate. Thus, measured 
water level r will be a function of water flow rate. 
Many variations of this invention are apparent. For 
example, aircraft borne radar could be substituted for 
l5 the orbiting radar, radar other than synthetic aperature 
radar could be used, multiple frequency and multiple 
polarization radar can be used as well as single fre- 
quency and polarization, various processing techniques 
From equation (21, the height of the water level Can be 2o can be used to define measurements and to identify 
determined by measuring relative reflector image targets, target designs can be modified to allow opera- 
brightness @rightness=flradar Cross-sectiOnl) in re- tion of radar at depression angles other than 45 degrees, 
motely sensed radar image. From a plot of relative and targets can be constructed or fabricated using mate- image brightness (add as a function of collected rials other than those specified in FIG. 1. 
water depth to cylinder height (rr) ,  this reflector 
concept can be expected to give reasonably sensitive 25 provides a global 
cent of the reflector cylinder height. 
of the invention in FIG. 
1 without a catch basin can be expressed as: 
( I )  a = 8  Ira H2 (Cos 4) A- * 
where: 
a = cylinder radius 
H=cylinder height 
+=incident wave angle from plane of flat base plate 
A = radar wavelength 
r= [l - ( a z / a l ) l ] H  
(ground plane) 
Thus, from FIG. 1 and equation (l), when 4=45" 
(2) 
where: 
r=depth of water in catch basin 
al=radar cross section with r=O 
az=radar cross section with r>O 
me advantages of invention are numerous. It 
monitoring capability; it uses 
ety of parameters needed for water status evaluations 
relative to weather and climate impact; it is simple and 
performance for (r) levels to 50 per- standard targets and system for measuring a wide vari- 
The number 21 in FIG. 2 designates an embodiment 
when used by itself at a se- 
and each time it passes Over the radar target z1 it provides some image views of ground sites and water 
takes an image of an area including the radar target. me sources; its images showing water sources are available 
brightness or intensity of the radar target image is in&- with measurement data; it makes changed detection 
ative of the level of water in the catch basin ofthe radar 35 data available; it requires only simple modification to 
target. From this information the rainfall, runoff, flow the basic target design to create a variety of different 
rate, evaporation, and soil moisture can be determined. target types for effecting multiple measurement; and it 
FIG. 3 shows a modified embodiment of the inven- does not require a calibrated radar. 
tion in which soil moisture can be measured. The em- What is claimed is: 
bodiment of the invention in FIG. 3 includes drain holes 40 1. A radar target for remotely measuring water status 
16 through the base plate and the concrete catch basin. at a selected location comprising: 
As water accumulates within this modified target, its a cylindrical radar reflector; 
discharge rate through the drain holes into the soil will a cylinder flat plate radar reflector symmetrically 
be proportional to the moisture content of the soil. As attached to the bottom of said cylindrical conduc- 
water is absorbed into the soil, r decreases and this 45 tor such that the central a i s  of said cylindrical 
change can be measured on successive image passes. A reflector is perpendicular to the plane of circular 
number of geographcally dispersed targets would be reflector; and 
required to assess overall soil moisture for any large a catch bash means including said cylindrical reflec- 
tor and said flat plate reflector for catching and area such as might be involved with desertification, but 
a single soil moisture target could be used to provide 50 retaining water and thereby providing a radar re- 
flector whose reflecting radar cross-section de- reference data for other remote sensing techniques. 
creases as the water level rises in said catch basin FIG. 4 shows a modified embodiment of the inven- 
means. tion in which the catch basin has been eliminated. The preferred techinque for gathering data or information 
by this invention is shown in FIG. 2. A radar target according to claim 1 wherein said 
bodiment ofthe invention in FIG. 4, shown in FIG. 5 as outer periphery of said catch basin means is slanted 
24, is included with an embodiment of the invention away from said cylindrical reflector whereby the edges 
shown in FIG. 1. These two radar targets are placed at of said catch basin means do not interfere with incoming 
a selected location on the surface of the earth. Conse- radar 
quently, when the satellite 22 makes an image of the 60 3. A radar target according to claim 1 including drain 
area including the targets 21 and 24 two bright spots holes through the base Plate and catch basin means 
will appear on the image. The relative intensities or whereby soil moisture can be determined by measuring 
brightnesses of these two spots is indicative of the the the rate water is absorbed by the soil. 
height of the water level in target 21 as per equation (2). 4. Apparatus for measuring the water status at a se- 
The relative intensities of the images of the two targets 65 Iected location on the surface of the earth comprising: 
can be determined by an individual's measurement ob- a radar target at said selected location having a radar 
servations or alternatively the relative intensities can be cross-section area for reflecting signals from a ra- 
determined automatically by a scanning means that dar; 
lected location on the surface of the earth. A satellite 22 30 low 
with a synthetic aperature radar 23 on board circles the 
it requires Only in the to 
be used and to be installed, maintained and operated; it 
in which an em- 55 
4,184,155 
5 6 
means included with said radar target for collecting 
water and for decreasing its radar cross-section 
area with an increase in collected water; 
view; and water status; 
means for moving said radar to a position for taking a radar with means for taking images of the area 
an image of an area on the surface of the earth that covered by the radar; and 
includes said radar target whereby the intensity of means for moving said radar to a position for taking 
the reflected energy from said radar target as deter- 10 an image of an area on the surface ofthe earth that 
includes said first and second radar targets mined by said image is indicative of the amount of 
whereby the relative intensity of the reflected en- water collected by said radar target. ergy from said first and second radar targets as 
5. Apparatus for measuring the water status at a se- determined by said image is indicative of the water 
lected location according to claim 4 wherein said radar 15 status at said selected location. 
is a synthetic aperature radar. 9. Apparatus for measuring the water status at a se- 
6. Apparatus for measuring the water status at a se- lected location according to claim 8 wherein said radar 
lected location according to claim 4 wherein said radar is a synthetic aperature radar. 
target includes a cylindrical radar reflector, a base plate 10- Apparatus for measuring water status according 
reflector symmetrically attached to the bottom of said 20 to claim 8 wherein said first radar target includes a 
cylindrical radar reflector and a flat circular plate radar cylindrical reflector such that the central axis of said reflector symmetrically attached to the bottom of said 
cylindrical reflector is perpendicular to the plane of said reflector such that the central axis of said 
base plate reflector, and a catch basin including said cylindrical reflector is perpendicular to the plane of said 
cylindrical reflector and said base Plate reflector for 25 flat base plate reflector and means for collecting water 
collecting water. including said cylinder reflector and said flat circular 
7. Apparatus according to claim 6 wherein said radar Plate reflector. 
target includes drain holes in its bottom whereby the 11- Apparatus according to Claim 10 wherein Said 
second radar target includes a cylindrical radar reflec- moisture in the soil can be measured. 
30 tor with a flat circular radar reflector symmetrically 
'* Apparatus for measuring the water status at a attached to the bottom of said cylindrical reflector such 
a first radar target at Isaid selected location having a pendicular to the plane of said flat circular plate reflec- 
radar cross-section area for reflecting signals from tor. 
a radar; 35 
means included with said first radar target for collect- 
ing water and for decreasing its radar cross-section 
area with an increase in accumulated water; 
a second radar target at said selected location having a radar with for taking images Of its 
Of 5 a radar cross-section area that is not changed by 
lected location on the surface of the comprising: that the central axis of said cylindrical reflector is per- 
* * * * *  
40 
45 
50 
55 
65 
UNITED STATES PATENT AND TRADEMARK OFFICE 
CERTIFICATE OF CORRECTION 
PATENT NO. : 4 , 1 8 4 ?  155 
DATED : J a n u a r y  1 5 ,  1980 
INVENTOR(S) : W i l f o r d  E.  S i v e r t s o n ,  J r .  
is hereby corrected as shown blow: 
It is certified that error appears in the aboveidentified patent and that said Letters Patent 
On t h e  cove r  page t h e  s p e l l i n g  of l l S i l v e r t s o n ,  J r . "  
s h o u l d  r e a d  -- S i v e r t s o n ,  J r .  --. 
Signcd and Scalcd this 
(SEAL1 
Attest: 
RENE 0.  TECTMEYER 
Acting Commissioatr of Patents and Trdemrkr 


Radar target for remotely sensing hydrological phenomena

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