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.