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How to use marine radar for bird watching

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RADAR TECHNIQUE
How to use marine
radar
for bird watching
A simpleand inexpensive
methodfor usinga
widelyavailabletypeof radar
Timothy C. Williams
ly approximate
an observerwith binocu-
OR
MORE
than
two
decades
haslarsin their ability to detectbirds (range
been
an important
tool in radar
ornithology. Radar detects the movementsof
birdsat night or in cloudsor fog, and
displaysthebirds'positionon a map-like
screenthatgivesa moreaccuratelocation
thanis possibleby meansof visualobservation with binoculars even under excel-
lent visibility conditions(see Eastwood
1967).
Many different sorts of radar have
been used for studyingbird migration:
airportradars,weatherradars,and even
satellitetrackingradars. In contrastto
these complex instruments,which requireseveraltrainedoperators,the common andeasilyoperatedsmall-boatmanne radar has largely been ignored by
ornithologists.Theseradarsare rugged,
dependableinstrumentswith fewer controlsthan a stereoradio receiver.In my
experiencea high schoolgraduatecan
learn to use them for observingbirds in
aboutonehour. The low powerradiation
of these instrumentsposeslittle or no
hazard, and thus they can easily be
moved from one location to another with-
about one kilometer, altitude, ground
level to about200 meters, seeCohen and
Williams 1980, for altitude estimation).
5) Turndownthebrightness
or
videogainuntil you canjust
seethecarpetof background
random noise on the screen.
Thereshouldbe severallarge,brightech-
Thus,it is oftenpossibleto identifyradar
echoesby visual meansduring the day
andthencomparetheseechoeswith those
seenat night. Suchidentificationis difficultor impossiblewith largeinstruments
(Williams and Williams 1980).
Marineradarsareby far the mostcommon type of radar, and usually it is not
difficultto obtainthe owner'spermission
to useone.Thereis noneedto modify the
radaror changeits calibrations;and, as
the radar can detect large numbers of
oes on the radar screen, which will be
birds in a few minutes, the time needed
birdswill moveabout1/10
of an inchbe-
for bird study is very small compared
with the normaloperationof the radar.
For thesereasonsmany boat ownersare
amenableto naturalists
usingtheirradars
for ornithologicalobservations.
tween successivesweeps (about 30
mph). This is sufficientfor each successiveimageon theradarscreento be separatedclearlyfrom the previousone. Echoes from boatsare usuallymuch larger
than those from birds, and move more
slowly,sothatthe successive
imagesare
not separated.Aircraft appear as large
INSTRUCTIONS
IRSTONEmustlearnto recognize
refreshedby eachsweepof the courseras
it movesaroundthedisplayandwhichdo
notchangepositionon the screen.These
are echoesfrom stationaryobjectssuch
asdocks,islands,or buoys,andone has
to learn to ignorethem. Echoesthat do
changepositionwith each sweepof the
courseraremovingobjectssuchasbirds
or boats.Birds are easily distinguished
by theirspeed.On a six-inchradarscreen
setat V2nauticalmile range,echoesfrom
echoes at successive intervals of a half an
outthe needof obtaininggovernmentapproval. This mobility usuallymore than
compensatesfor the relatively short
rangeat which theseinstrumentscan de-
birdson theradardisplay.I suggesta
calm day when severallarge birds, such
as waterfowl or gulls, are moving over
the water about 100 to 300 meters from
inchor more.Oncepresumedbird echoes
are detected,they may be verified by
checkingwith a pair of binocularsat the
distanceand direction indicatedby the
tect birds, about one kilometer. Marine
the radar.
radar.
radarsare designedfor high resolution
work;theentiredisplaycanbe setto cover only two kilometers. At this resolution, V's of geese,flocksof blackbirds,
andsinglepasserinemigrantsare clearly
recognizable
on a marineradar(Williams
and Klonowski 1974), but would all appear as a singledot on the displayof a
largerradar set at its minimum rangeof
10 to 50 kilometers.
982
Marine radars close-
1) Turn on the radar and let it
warm up.
2) Setrangeat V2nauticalmile
or one kilometer.
Thereareseveralmethodsof recording
radardata.The simplestis to observethe
radar screen directly and record the
speed, direction, and location of bird
3) Set all anti-rain and anti-sea
echoes on the radar screen. I find this is
return controls to minimum.
mosteasilydonewith a clearplasticruler
placedparallelto theline of dotsmarking
a bird trackon the radardisplay. At night
4) Set receiver gain to maximum.
The
screen
should
now be very bright, almost
or if the radaris in a dark room, thesedots
all white.
will persistfor severalrevolutionsof the
American Birds, November-December 1984
A
B
C
A radarfenceallowsa marineradar to detectbirdsoverwavesor land areas.Eachof thethreeparts ofthisfigureshowsa diagrwnof a boatwitha
radarunderdt•fferent
conditions.Thebeamof theradar is shownjust as it sweeps
pastthefront of theboat. Thecirclebeloweachdiagramshowsthe
screenof theradar as it wouMappearin thatsituationafter severalrotationsof theradar beam.Theradar displayreadslike a mup,withtheboatat
therenter,objectsinfront of theboattowardthetopof thescreen,and objectsbehi,d theboattowardthebottomof thescreen.A. The radar easdy
dete•tsa bird.flyingovercalmwater;thetrackof thebird isshownas a seriesof dotson theradar screen.B. Theboatis sin'rounded
by wavesandthe
rada•eehoes
from thesewaves(thelinesof dotson thescreen)obscurethetrackof thebird. C. Theboatispositionedbehinda longsandbur,whkh
at tvasa radarfence,eliminatingechoes
from wavesbeyondthebar.Thesandbarproduces
a long,whiteechoon theradar screen,andechoes
from
waves'can still be seenin the lower half of the screen,but beyondthe sandburthe screenis clear and the track of the bird is easilydetected
radar courser. The direction of travel rel-
ativeto theboatis readdirectlyfrom the
compass
roseon the circumferenceof the
radar screen.Speedis calculatedfrom
d•stance traveled in four or more revolu-
tionsof the courser,the revolutionsper
mtnutebeingconstant.With this method
•t •s difficult
to follow
more than two
b•rdsat a time. A morecompleterecord
may be obtainedby makingtime-lapse
ctne films of the radar screen. A detailed
comparison
betweena time-lapsefilm
analysis
andnotesmadedirectlyfromthe
radar screen has shown that the two meth-
odsare in excellentagreementand that
for mostpurposesdirect observationof
the radar will yield sufficientaccuracy
(Wdliamset al. 1981). During heavy
nocturnalmigrationit is usualto have
five to ten birds on the radar screen at one
t•me Ten minutes of visual observation
from terrestrialobjectsby reducingthe
sensitivityof the radar to objects at
groundlevel.Thisis easilydoneby positioningtheradarcloseto a low building,
a sanddune,or otherradar-opaque
object
thatcutsoff thatportionof theradarbeam
parallelto the ground,leavingonly the
portionof the beamwhich is angledupward towardthe sky. This resultsin a
strongecho from the radar fence (the
nearbyobject),but a clear radar screen
beyondtheradarfence.Avoidusingvertical cliffs or high walls as a radar fence
astheyreflecttoo muchenergybackto
theradarandreducesensitivity.
Treesin
leaf, sanddunes,or slopingroofsare all
excellent.
Anotherproblemis motionof theboat.
Sincemostradar displaysshowechoes
relativeto the boat, a movingboat will
causeevenstationary
objectsto moveon
wouldyieldmorethan50 tracks,usually
enough
for a reliableestimateof themean
&rectionandspeedof migration.
The instructionsabove are adequate
whenthewateris calm, but thisis rarely
the radar screen. This is eliminated, of
the case, and the use of a radar fence,
portantto comparediurnaland nocturnal
activity, to examinelocal movementsof
birds,orto examinemigratorypatternsin
whichpermitsobservation
underwindy
conditionsor over land areas, must be
&scussed.
Any objectthatreflectssufficmntradarenergywill showas an echo
on the radar screen;this includeswaves,
landareas,anddocks.Thesestrongechoes will obscure the much fainter echoes
of b•rdsif they are locatedin the same
areaof thescreen.Sincewe are onlyinterestedin birds, we can cut off echoes
Volume 38, Number 6
course,if theboatis securelyanchored
in
a protectedlocationor tied up at a dock.
Marine radars will be most useful for
ornithological
studiesin whichit is im-
remoteareas.In my opinionthe longer
rangeof more powerful radar installationsis over-rated;estimatesof migratory directionand speedwith marineradarsdonotseemto be anymorevariable
than those taken with surveillance radars
having100 timesmorerange(Williams
et al. 1981). The principaladvantageof
greaterrangeseemsto be detectingbirds
flying at greateraltitudes.On thoseunusualnightswhenbirdsat differentaltitudeswouldshowdifferentmigratorybehavior,thenthemarineradarsgivea less
completesample.
LITERATURE
CITED
COHEN, B. and T. C. WILLIAMS
1980. Migrant bird trackson search
radars: Short range corrections.J
Field Ornithol.
51: 248-253.
EASTWOOD, E. 1967. Radar Ornithol-
ogy. Methuen and Co., London.
278pp.
WILLIAMS,
T. C. and T. J. KLON-
OWSKI. 1974. Flight patterns of
birds studied with an Ornithar.
Proc
of Conferenceon the biological aspects of the bird/aircraft collision
problem.U.S.A.F. Office of Scientific Research.
WILLIAMS,
T. C. and J. M. WIL-
LIAMS. 1980. A Peterson'sguideto
radarornithology?
Am.Birds34: 738741.
WILLIAMS, T. C., J. E. MARSDEN,
T. L. LLOYD-EVANS, V. KRAUTHAMER
and H.
KRAUTHAMER
1981.Springmigration
studied
by mistnetting,ceilometerandradar.J. Field
Ornithol.
52: 177-190.
---Department of Biology,
Swarthmore College,
Swarthmore, PA 19081
983
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