A POCKET FIRE-SIZE ESTIMATOR FOR AERIAL OBSERVERS

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2 A POCKET FRE-SZE ESTMATOR FOR AERAL OBSERVERS BY J. NEDERLETNER NFORMATON REPORT NOR-X-157 JUNE 1976 NORTHERN FOREST RESEARCH CENTRE CANADAN FORESTRY SERVCE ENVRONMENT CANADA STREET EDMONTON, ALBERTA, CANADA T6H 3S5

3 Niederleitner, J A pcket fire-size estimatr fr aerial bservers. Envirn. Can., Envirn. Manage. Serv., Nrth. Fr. Res. Cent. nf. Rep. NOR-X-lS7. ABSTRACT A pcket-size sighting tl can easily be fashined frm a 22. S-cm length f 3-mm welding rd. With it aerial bservers can estimate grund distance and areas as a functin f the aircraft's altitude. RESUME On peut facilement fabriquer un "stadimetre" de pche a incendies de frets avec un tige de sudure lngue de em et a diametre measurant 3 mm. Avec ce simple instrument, l'bservateur vyageant en avin peut estimer la distance au sl et la superficie de l'incendie en fnctin de l'altitude de l'avin.

4 NTRODUCTON TABLE OF CONTENTS Page 1 THE POCKET ESTMATOR Principle f Operatin Descriptin APPLCATON REFERENCES t 8 POCKET ESTMATOR, NSTRUCTONS, AND AREA CALCULATONS TABLE nside Back Cver

5 NTRODUCTON Aerial bservers must ften estimate the size f features n the grund, such as the area f frest fires r the length f fire guards r retardant drps, withut a suitable map prviding the details needed t establish a size relatinship. Unrealistic estimates f initial fire size can result in the dispatch f insufficient r excess suppressin frces and, entered int the fire reprt frms, cmplicate the statistical evaluatin f fire data. THE POCKET ESTMWTOR PRNCPLE OF OPERATON A device (Fig. 1) was invented t assist the aerial bserver r pilt in estimating the size f grund features bserved frm the aircraft. The Pcket Estimatr is based n the principle f similar triangles under the assumptin that the flying height ver the feature t be measured is knwn (Fig. 2). The abve-grund altitude (H-h) can be calculated fairly accurately by subtracting the grund elevatin (h) as marked n the map frm the temperature-crrected altimeter altitude (H). The Pcket Estimatr des nt measure areas directly, it nly prvides a reference fr lengths. Areas must be calculated frm the established linear dimensins. The Pcket Estimatr is basically an angle gauge similar t a stick hypsmeter (Chapman and Meyer 1949) r a Biltmre stick, but instead f a graduated stick the Pcket Estimatr emplys a smth sighting pst (Fig. 3) prprtined s that its length cvers a distance n the grund equal t ne-half f the flying height. A psitining arm keeps the

6 2 F 1. The Pcket Estimatr, flat and cmpact t fit int shirt pckets. si ing pst at a cnstant distance frm the eye. The end f the psitinrd is bent t frm a safe eye rest and a handle, used t steady the Pcket Estimatr t the bserverfs cheekbne (Fig. 1). Because the sighting pst is 10 em frm the eye it lks smewhat blurry when ne sights ver it. This results in a certain margin fr errr when prjecting the pst ends t the Hwever, cnsidering that the ther factrs influenc area estimates, as the irregular perimeter f areas t be measured, distance, and b queness f the area in relatin t pint f bservatin are als tins, the Pcket Estimatr is within the range f required precisin.

7 - --- ' <) "".,.",,,, O.lm b E ") E E ") E g, (H-h) SOOm 1000m 2000m b = (H-h) b 2 a = - a = measured distance n grund b flying height abve grund h = grund elevatin H indicated altimeter altitude Figure 2. The Pcket Estimatr is a simple tl f triangulatin. w

8 4 /) 14t l0cm f T, EYE REST HANDLE i _ POSTONNG ARM 5.5'm _ l /) 0.. Z - J: SCALE: AC TUAL SZE 5cm FG. 3 Figure 3. Dimensins f the Pcket Estimatr DESCRPTON The Pcket Estimatr cnsists f a 22.S-cm (9-in. ) length f 3-mm (lb-in.) diameter mild steel welding rd bent as shwn in Fig. 3 t frm a sighting pst, psitining arm, eye rest, and handle. All bends are n the same plane t keep the device flat. ts uter dimensins are nly 5 cm (2 in. ) by 10 cm (4 in.), s that it fits readily int a shirt pcket, ntebk, r map flder. t is painted with black flat blackbard paint t eliminate unwanted reflectins, with a dab f white paint at either end f the

9 5 sighting pst t help in sighting. Luminus white paint culd be cnsidered fr night bservatins by airline pilts. APPLCATON T take a measurement the bserver hlds the estimatr by the handle and presses the eyer est firmly against his cheekbne immediately belw his eye scket. Lking ver the sighting pst vertically dwn at the fire (r any ther target) n the grund, the bserver cmpares the target size t the length f the sighting pst. Fr the purpse f measuring, the shape f the fire shuld be simplified int ne r mre squares r circles, and then the side f the square r the diameter f the circle measured in sighting pst lengths (Fig. 4). t is useful t draw a rugh sketch f the fire and shw n it the sighting pst lengths fr later reference. D nt frget t mark dwn the altimeter altitude. - \, "? c::::;... :::::,:: T---_ i _ SGHTNG POSTS 1/ - i... ' 11 i! FRE AREA L :---==t:-:==-==.:-=---' " \ /1 MAGNARY SQUARES \ / 1 / , '--_/ - Figure 4. Divide fire mentally int squares r circles. Mark psitin f measured sighting pst lengths as well as the altimeter reading fr later reference.

10 6 The area fr each square and circle is then calculated as fllws: 1) Establish the distance cvered n the grund by ne sighting pst length. t always equals ne half f the aircraft's altitude abve grund: 2) (H-h) 2 Using either frmula P(H-h) r PT (H-h) 2 4" 2 where: H = altimeter altitude h P grund elevatin f target area sighting pst length calculate the area f the square r circle in square metres. deally the aircraft's altitude shuld be selected t simplify area calculatins. Fr example, if the altitude abve grund is 200 m then ne sighting pst length cvers n the grund 100 m, which is the side f a 1-ha square (100 x 100 m). 3) f the feature t be measured was divided int segments, calculate the area fr each segment, ttal the number f square metres, and cnvert them int hectares (1 ha = m 2 ). Multiply the number f hectares by 2. 5 fr an apprximate cnversin int acres. Table 1 cntains calculated square and circular areas fr varius measured sighting pst lengths paired with altitudes in metres. The pcket n the inside back cver cntains ne Pcket Estimatr with perating instructins and an abbreviated area calculatins table.

11 Table 1. Area calculatins fr Pcket Estimatr Aircraft Altitude (metres) Grund distance cvered by ne sighting pst length (metres) ha P Calculated area fr given number sighting Est lengths (P) Fr square areas! Fr circular areas 2 1P 2p P 1P acre ha acre ha acre ha acre ha acre ha 2P a.c:..e lloo , , llo llo ll P = side f square 2 P = diameter f circle...

12 8 REFERENCES Chapman, H. H. and W. H. Meyer Frest mensuratin. American Frestry Series. McGraw Hill. New Yrk. 522 pp.