Field, Backcountry, and SAR

Tools in this group

• Pacing and Distance - Distance from pace count with terrain correction; reference table per stride length.
• Magnetic Declination and Bearing Conversion - Magnetic-to-true and true-to-magnetic with east-is-least / west-is-best memo.
• Slope Angle and Avalanche Risk Window - Slope angle, slope %, and 30-45 deg avalanche start-zone flag.
• Backcountry Water and Caloric Requirement - Water (L) and kcal per person per day with trip totals.
• UTM and Lat-Lon Conversion - Krueger / USGS deterministic forward and inverse formulas (WGS84).
• Sunrise, Sunset, and Civil Twilight - NOAA solar-position algorithm: sunrise, sunset, civil / nautical / astronomical twilight, daylight minutes.
• Lightning 30-30 Rule Countdown - NWS 30-30 rule: seconds between flash and thunder -> distance in miles and seek-shelter advisory. Sound speed ~1125 ft/s.
• Magnetic Declination (WMM2025) - Local magnetic declination, inclination, field intensity, and annual change from latitude, longitude, date, and (optional) altitude. NOAA NCEI World Magnetic Model 2025; valid 2025-2030. Bearing-correction helper built in.
• Search Probability of Detection - Cumulative probability of detection across search passes, probability of success (POS = POA x cumulative POD), and residual containment probability for SAR planning.
• Search Track Spacing and Coverage - Single-pass probability of detection from corrected sweep width and track spacing (coverage = W/S, POD = 1 - e^-coverage), or the spacing that hits a target POD. The planning number a search segment's resources are set from.
• Sweat Rate and Fluid Replacement - Personal sweat rate and rehydration target from a weigh-in/weigh-out (sweat_loss = (pre-post) x 16 + fluid - urine), with the percent body-weight loss flagged against the 2% performance-degradation line. Sets a drinking plan for the next shift.
• Search Effort in Searcher-Hours - What sweeping a segment actually costs: track_ft = 43,560 x acres / spacing, effort = track_ft / (mph x 5,280) in searcher-hours, and the team clock time = effort / searchers. A 160-acre segment at 40 ft spacing is 33 miles of track line - 22 searcher-hours at 1.5 mph, or 2.75 clock hours for a team of eight, before briefing, travel, and rest. Prices the spacing that search-track-spacing sets for a POD, so segments get sized to the resources. A planning aid, not a promise of coverage.
• Sweep Width Correction (Weather, Speed, Fatigue) - The effective sweep width the searchers actually have: W = uncorrected width x weather factor x speed factor x fatigue factor (IAMSAR / US National SAR Supplement practice). A 120 ft raw detection width in rain with a tired crew (weather 0.5, fatigue 0.9) is a 54 ft effective width - a 55% haircut before the first track is walked. Produces the corrected W that search-track-spacing expects, so the spacing gets planned against real conditions. A planning aid, not a promise of detection.
• Area by Coordinates - Enclosed area, perimeter, and winding of a closed traverse by the shoelace method.
• Traverse Closure and Adjustment - Latitude and departure misclosure, relative precision, and compass-rule adjusted coordinates.
• Hiking Time (Naismith's Rule) - Backcountry / SAR trip-time estimate by Naismith's rule: horizontal distance / pace plus 1 hour per 600 m (about 2000 ft) of ascent, scaled by a terrain / fatigue factor, reported in hours and h:min (first-principles plus the canonical Naismith ascent rate; a planning estimate, distinct from pacing-distance which gives distance from a pace count).
• Differential Leveling (HI Method) and Loop Misclosure - The vertical control the traverse tiles never carried: differential leveling reduces backsight/foresight rod readings by the height-of-instrument method (HI = elev + BS, elev = HI - FS) to carry an elevation from a benchmark across a site, and checks a loop for misclosure. A BM at 100.00 ft with backsights 4.32 / 5.60 and foresights 2.15 / 3.40 closes at 104.37 ft, the sum(BS) - sum(FS) rise the field book is balanced against; close on a known 104.40 and the -0.03 ft misclosure is the pass/fail. Arithmetic reduction, no adjustment distribution. A computational aid; the project control governs.
• Level-Loop Misclosure Distribution (Compass Rule) - The step differential leveling leaves out: spread a level-loop misclosure back across the benchmarks so the loop closes. Correction to each point = -misclosure x (distance leveled to it / total distance) - the vertical analog of the compass rule the traverse tile uses. A three-leg loop closing 0.05 ft high over 2,000 ft puts -0.0125 ft on the first point at 500 ft and the full -0.05 ft on the last, so the adjusted elevations land exactly on the known benchmark. Distance-weighted; equal-weight-per-setup is an alternative. A computational aid; the project control governs.
• Stadia Tacheometry (Distance and Elevation) - The classic instrument method of reading a distance and rise off a rod interval, still used for topo checks: with K = 100, the horizontal distance H = K s cos^2(theta) and vertical V = (K s/2) sin(2 theta) from the stadia interval s and vertical angle. A 1.50 ft interval at +5 degrees gives 148.9 ft and a 13.0 ft rise; on a level sight it reduces to the bare H = 100 s with no rise. Internal-focusing instrument (C ~ 0), no curvature/refraction correction. A computational aid; the instrument's stadia constants govern.
• Steel Tape Distance Corrections (Temperature, Slope, Tension, Sag) - The difference between a rough measurement and survey-grade distance: a steel tape's corrected length is the measured value plus four corrections - temperature Ct = alpha (T - T0) L (alpha 6.45e-6 /degF), slope Ch = -h^2/(2L), tension Cp = (P - P0) L/(A E), and sag Cs = -w^2 L^3/(24 P^2). A 100 ft tape read at 95 F down a 3 ft grade corrects to 99.972 ft (warm tape reads short, +0.017; slope -0.045); a cold tape flips the temperature sign. The systematic bias a warm-day traverse carries throughout. A computational aid; the tape calibration governs.
• COGO Forward Locate (Bearing and Distance) - The single COGO step traverse-closure only ever sums over a loop: from a known point, an azimuth (clockwise from north), and a distance, the new coordinates. Latitude dN = D cos(Az), departure dE = D sin(Az); N2 = N1 + dN, E2 = E1 + dE. From N5000/E5000 at azimuth 45 deg over 200 ft the point lands N5141.42/E5141.42. Convert a quadrant bearing (N45E) to azimuth first (bearing-conversion). Plane geometry - no curvature or grid scale factor; the project control and datum govern.
• Total-Station Slope-to-Horizontal Reduction - The right-triangle reduction of an EDM/total-station slope distance to horizontal distance and elevation: with a zenith angle Z, H = S sin Z and V = S cos Z; with a vertical angle a, H = S cos a and V = S sin a; ground-to-ground elevation difference = V + instrument height - reflector height. A 250 ft slope shot at an 86 deg zenith is 249.39 ft horizontal and 17.44 ft up. The step that feeds the horizontal distance to cogo-forward-point. No curvature/refraction or grid scale factor; the instrument and control govern.
• State-Plane Grid-to-Ground Distance - The grid scale factor the COGO and slope tiles say they skip: elevation factor EF = R/(R+h) with R = 20,906,000 ft, combined factor CF = grid-scale-factor x EF, and ground = grid / CF. A 10,000 ft grid distance at a 0.9999 scale factor and 5,280 ft ellipsoid height is 10,003.53 ft on the ground. Enter the ellipsoid height h = orthometric elevation H + geoid height N (N ~ -30 m in the US), not the elevation alone. Per the NGS State Plane Coordinate System; the published control governs.
• COGO Inverse (Two Points to Bearing and Distance) - The exact inverse of the cogo-forward-point tile: from two known points, the straight-line distance and the azimuth of the line between them. distance = sqrt(dN^2 + dE^2), azimuth = atan2(dE, dN) clockwise from north; dN = N2-N1, dE = E2-E1. From N5000/E5000 to N5141.42/E5141.42 the line runs 200.00 ft at azimuth 45.00 deg. Read it as a quadrant bearing with bearing-conversion. Plane geometry - no curvature or grid scale factor; the project control governs.
• Leveling Curvature-and-Refraction Correction - The correction the leveling and slope-reduction tiles say they skip: with K the sight distance in thousands of feet, curvature raises 0.0239 K^2 ft and refraction bends back 0.0033 K^2, leaving a net 0.0206 K^2 ft subtracted from the far rod. A 2,000 ft sight is 0.0824 ft. Balanced backsight/foresight cancel it; a long or unbalanced sight and reciprocal/trig leveling do not. Assumes refraction k ~ 0.14; the project procedure governs.