Estimate Reference Noise Limits in Normalized Doppler Frequency

This function estimates the reference noise limits for normalized Doppler frequencies in a SeaSondeR cross-spectral object. These limits define the frequency range over which the noise floor is assessed for first-order region (FOR) detection.

Usage

seasonder_estimateReferenceNoiseNormalizedLimits(
  seasonder_cs_object,
  low_limit = 0.95,
  high_limit = 1
)

Arguments

seasonder_cs_object

A SeaSondeRCS object containing Doppler frequency metadata.

low_limit

Optional. A numeric value representing the fraction of the maximum normalized Doppler frequency to be used as the lower bound for noise estimation. Default is 0.95.

high_limit

Optional. A numeric value representing the fraction of the maximum normalized Doppler frequency to be used as the upper bound for noise estimation. Default is 1.0.

Value

A numeric vector of length two, representing the lower and upper reference noise limits in normalized Doppler frequency.

Details

The function operates as follows:

1. Retrieves the Doppler bin frequencies in normalized units (relative to the Bragg frequency) via seasonder_getDopplerBinsFrequency.

2. Computes the noise limits by scaling the maximum normalized Doppler frequency using the provided low_limit and high_limit factors:

   • The lower bound is given by max(freq) * low_limit.

   • The upper bound is given by max(freq) * high_limit.

3. The default empirical choice for the lower bound (56.5% in the original calibration process) is adjustable via the low_limit parameter. This parameter was determined through an iterative process where the initial lower bound was decreased in increments (e.g., 0.5%) until the computed noise floor closely matched the reference provided by the AnalyseSpectra Tool in Radial Suite R8.

This approach is crucial for setting the signal-to-noise ratio (SNR) thresholds used in FOR detection.

See also

seasonder_getDopplerBinsFrequency for retrieving Doppler bin frequencies.