Slope Factor Rate of Spread Cosine Calculator
Cosine project actual along-slope front motion onto horizontal run, not a guessed fire acceleration/slope enhancement factor. Caller independently verifies units, applicability and matching conditions; no operational recipe, safety certification, causal efficacy or legal/resource classification is inferred.
Description
Along-slope distance and horizontal distance differ by the cosine of slope angle.
Along-slope distance and horizontal distance differ by the cosine of slope angle.1
Projecting a measured spread speed changes its geometric component without modeling how slope changes fire behavior. Use this tool to calculate slope factor rate of spread cosine from the supplied measurements and assumptions.
When to use Slope Factor Rate of Spread Cosine Calculator
Use this tool to calculate slope factor rate of spread cosine from the supplied measurements and assumptions. Establish the species/site, survey protocol, units, sampled area or exposure, and the independently chosen reference or model.
How to use Slope Factor Rate of Spread Cosine Calculator and understand its results
- Establish the species/site, survey protocol, units, sampled area or exposure, and the independently chosen reference or model.
- Enter observedAlongSlopeSpreadMSecond, observedSlopeAngleDegrees, using the field meanings and rules below, then run the tool.
- Read horizontalProjectedSpreadMSecond. Interpret the fields using their units, signs and evidence conventions below.
- If input validation fails, correct the reported field and run again. Before applying the result, check reference scope, model assumptions and any missing evidence or placeholder values.
| Input field | Meaning | Value type | Requirement |
|---|---|---|---|
| observedAlongSlopeSpreadMSecond | Observed along slope spread m second | list of number | Required |
| observedSlopeAngleDegrees | Observed slope angle degrees | list of number | Required |
Enter nonnegative observed along-slope spread speeds and matched signed slope angles strictly between −90 and 90 degrees. Multiply each speed by cosine of the angle in radians and retain its units. This is projection only; neither slope acceleration nor a fire-spread model is applied.
horizontalSpeed_i=alongSlopeSpeed_i×cos(slopeDeg_i×π/180) Use the exact units, boundary rules, ordering and missing-evidence conventions above.
| Output field | Meaning | Value type |
|---|---|---|
| horizontalProjectedSpreadMSecond | Horizontal Projected Spread M Second; follow the units, sign, ordering and evidence convention stated above | list of number |
{
"input": {
"observedAlongSlopeSpreadMSecond": [
1,
2
],
"observedSlopeAngleDegrees": [
0,
60
]
},
"output": {
"horizontalProjectedSpreadMSecond": [
1,
1.0000000000000002
]
}
}Limitations and assumptions
Projecting a measured spread speed changes its geometric component without modeling how slope changes fire behavior. Interpretation depends on the units, sampling scope and exact model described above.
All listed fields require explicit values. Unexpected fields, incorrect types, nonfinite numbers and sparse evidence arrays fail validation; the specific bounds and alignment requirements are stated above. Extremely large inputs or outputs can also be rejected. An input error is distinct from a successful result reporting false, no matches or missing evidence.
Alternative or Complementary methods
Use Rothermel Surface Rate of Spread Calculator for this related task: A Rothermel-style spread relation balances reaction intensity and propagation factors against the energy needed to heat fuel.
Use Active Crown Fire Spotting Distance Calculator when its separate inputs and assumptions fit the question: Integrating horizontal wind over an independently sampled ember flight time gives a conditional advection displacement.
References
Similar or alternative tools
- Rothermel Surface Rate of Spread Calculator
A Rothermel-style spread relation balances reaction intensity and propagation factors against the energy needed to heat fuel.
- Active Crown Fire Spotting Distance Calculator
Integrating horizontal wind over an independently sampled ember flight time gives a conditional advection displacement.