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Default First-Order Radial Processing Parameters

Source: R/SeaSondeRCS_FOR.R
seasonder_defaultFOR_parameters.Rd

This function returns a list of default parameters for first-order radial processing in CODAR's Radial Suite R7. Each parameter has an equivalent R8 version, where applicable, often expressed in decibels (dB).

Usage

seasonder_defaultFOR_parameters()

Value

A named list containing the default parameter values.

Details

Parameter Descriptions:

  1. nsm (R8: Doppler Smoothing)

    • Default value: 2

    • Usage: Sets how many Doppler bins (points) are smoothed. Smoothing helps remove jagged edges in the sea echo spectrum, aiding in locating the null between the first and second order (or noise floor).

    • Recommended values: Typically 2 to 6. Default in Radial Suite R8 is 2

    • Effects of over-/under-smoothing:

      • Too high: May smear out the real null, causing the first order to appear wider.

      • Too low: Jagged minima may cause the null to be detected inside the first-order region, making it appear too narrow.

  2. fdown (R8: Null Below Peak Power)

    • Default value (R7): 10

    • Equivalent in dB (R8): 10 dB

    • Usage: Defines how far below the peak power the algorithm must descend (in dB) before searching for the null that separates the first and second order. This helps avoid including second-order energy as part of the first-order.

    • Recommended range: 3.981072 to 31.62278 (6 to 15 dB in R8). Default in Radial Suite R8 is 10 dB

    • Effects of misconfiguration:

      • Too large: The null search may be bypassed entirely, causing second-order content to be included in the first order.

      • Too small: The null may be found inside the first-order region, excluding valid Bragg energy.

  3. flim (R8: Peak Power Dropoff)

    • Default value (R7): 100

    • Equivalent in dB (R8): 20 dB

    • Usage: Once a peak is located, any spectral bins that are more than flim below the peak (in linear scale) or 20 dB below the peak (in dB scale) are excluded from the first-order region.

    • Recommended range: 15.84893 to 316.2278 (12 to 25 dB in R8). Default in Radial Suite R8 is 20 dB.

    • Effects of misconfiguration:

      • Too high: May include non-Bragg signal and yield spurious high velocity estimates.

      • Too low: May cut out part of the actual Bragg signal, underestimating maximum velocities.

  4. noisefact (R8: Signal to Noise)

    • Default value (R7): 3.981072

    • Equivalent in dB (R8): 6 dB

    • Usage: Sets the threshold above the noise floor that must be exceeded for the algorithm to accept Doppler bins as potential first-order.

    • Recommended range: 3.981072 to 7.943282 (6 to 9 dB in R8). Default in Radial Suite R8 is 6 dB

    • Effects of misconfiguration:

      • Too high: Useful Bragg data could be excluded.

      • Too low: Noise or spurious signals may be included as Bragg.

  5. currmax (R8: Maximum Velocity)

    • Default value: 2 m/s

    • Usage: Sets a maximum radial velocity, preventing first-order limits from extending beyond realistic current speeds for the site.

    • Effects of misconfiguration:

      • Too high: May include non-Bragg data, producing overestimated velocities.

      • Too low: May exclude valid Bragg data, underestimating velocities.

  6. reject_distant_bragg (Reject Distant Bragg)

    • Default value: TRUE

    • Usage: Rejects a first-order region if its limits are farther from the Bragg index (central Doppler bin for zero current) than the width of the region itself. Helps avoid misclassifying strong but isolated signals (e.g., ships) as Bragg.

    • Recommendation: Usually keep this enabled unless operating at a site where only strongly biased positive or negative currents are expected.

  7. reject_noise_ionospheric (Reject Noise/Ionospheric)

    • Default value: TRUE

    • Usage: Rejects Bragg if the total non-Bragg power in a range cell exceeds the Bragg power by at least the threshold set in reject_noise_ionospheric_threshold. Recommended to set as FALSE for 42 MHz systems.

    • Recommendation: Enable if the site experiences significant noise.

  8. reject_noise_ionospheric_threshold (Reject Noise/Ionospheric Threshold)

    • Default value: 0

    • Equivalent in dB: 0 dB

    • Usage: Difference threshold (in dB) for comparing non-Bragg power to Bragg power. If non-Bragg power is higher by this threshold, the Bragg is rejected.

    • Recommended setting: Typically 0 dB. Increase only if needed to be less sensitive to noise contamination.

References

COS. SeaSonde Radial Suite Release 7; CODAR Ocean Sensors (COS): Mountain View, CA, USA, 2013. COS. SeaSonde Radial Suite Release 8; CODAR Ocean Sensors (COS): Mountain View, CA, USA, 2016.

Examples

params <- seasonder_defaultFOR_parameters()
print(params)
#> $nsm
#> [1] 2
#> 
#> $fdown
#> [1] 10
#> 
#> $flim
#> [1] 100
#> 
#> $noisefact
#> [1] 3.981072
#> 
#> $currmax
#> [1] 2
#> 
#> $reject_distant_bragg
#> [1] TRUE
#> 
#> $reject_noise_ionospheric
#> [1] TRUE
#> 
#> $reject_noise_ionospheric_threshold
#> [1] 0
#>