HPE and Bias HPE - OCLO
HPE and Bias HPE - User References
This page is meant to supplement training material on the High-resolution Precipitation Estimator (HPE) and Bias HPE products. Please visit the HPE and Bias HPE Focal Point page for configuration details.
- Dual-Pol Source
- Y : precip source is Dual-Pol Digital Precip Rate (DPR) --> default
- N : precip source is Legacy Digital Hybrid Reflectivity (DHR)
- Bias Source
- RFC : mean-field bias from RFC MPE
- [WFO site ID] : mean-field bias from local site’s MPE --> default (see bugs below)
- [WFO site ID] Local Bias : local bias from local site’s MPE (spatially varying bias using 40-km search radius)
- Radar bias factors and # of gauge-radar pairs (e.g. kfws 0.50/12)
- Bias Factor : mean-field bias factor (explained in next section)
- Gauge-Radar pairs : # of pairs used to calculate the mean-field bias (minimum = 10)
NOTE: The bias factors and gauge-radar pairs list will only appear if one of the two mean-field bias sources is chosen.
- Current bugs in the labels (as of Dec 2020)
- Bias Source reads "RFC" but most offices are not receiving RFC bias information due to bugs in the AWIPS code. Please contact Mike Magsig for details on how to fix this.
- Therefore, most offices are receiving mean-field biases from their local MPE (even though the Bias HPE label says "RFC")
- The number of gauge-radar pairs are incorrect.
- They frequently say that a bias was calculated with less than 10 pairs, but it is not. Ignore the pair information and only interpret the bias factor.
- Bias factor is multiplicative
- > 1 : precip source is underestimating
- < 1 : precip source is overestimating
- Example: A bias factor of 2.0 means that the QPEs are under-estimating and need to be multiplied by 2.0 to bring them up to where they should be
- New hourly bias information comes in 25 minutes past the hour
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From the “SCAN” menu, identify the “FFMP” section, and select the FFMP Table/Basins Display menu item from the desired precip source menu (e.g. HPE, koax, etc.)
NOTE: There is a menu labeling error once you get to the HPE/BHPE menu. The FFMP Table is described as a “DHR MOSAIC”, and the menu should read “DPR MOSAIC”.
- Sources --> SfcGrid
- Choose “BiasHPE” and/or “HPE”
- Fields -->Sfc/2D --> Precip
- Choose either “Storm Tot Precip” and/or “Precip Rate”
- Planes --> Misc --> Sfc
The HPE/Bias HPE product from the Volume Browser is a contour product, so to convert to an image for viewing/sampling, right-click the product legend on the bottom right and select “Load as Image”.
The RPG can be configured (via the HCI) to apply a mean-field bias from MPE in the 1hr, 3hr, and storm total Legacy precipitation radar products (default is not to apply any bias in the routine radar products at the RPG).
- Check if the bias has been applied at the RPG
- Load the SCAN Precipitation Rate product for a particular radar (if this overlay has been configured by your focal point).
- The legend in the upper left will have the label: “Bias Applied Flag (T/F):”
- Load the SCAN Precipitation Rate product for a particular radar (if this overlay has been configured by your focal point).
- To enable the Bias Applied Flag overlay, the focal point or user can create an override in the Localization perspective:
- D2D --> SCAN --> config --> PrecipRate --> SCANconfig_precipRate.xml
- Have focal point make a site override copy of the base file or the user can make a copy to a user override
- Setting the bias flag to “True” adds it to the Precip Rate text overlay
- What is the High-Resolution Precipitation Estimator (HPE)?
- Mosaic of precip estimates from multiple radars with 1km x 1km resolution every 5 minutes, designed for use with FFMP when needing to analyze multiple radars at once.
- Can be based on Dual-Pol Digital Precipitation Rate (DPR) OR Legacy Digital Hybrid Reflectivity, but Dual-Pol is default.
- No bias has been applied to the precip estimates.
- What is the Bias High-Resolution Precipitation Estimator (Bias HPE)?
- Mosaic of bias-corrected precip estimates from multiple radars and rain gauges with 1km x 1km resolution every 5 minutes, designed for use with FFMP when needing to analyze multiple radars at once.
- Can be based on Dual-Pol Digital Precipitation Rate (DPR) OR Legacy Digital Hybrid Reflectivity, but Dual-Pol is default.
- Bias in Bias HPE is updated hourly at ~25 min after the hour continuously (24hrs a day), and the local hydro focal point can configure bias to come from (see first section).
- What is the High-Resolution Precipitation Nowcaster (HPN)?
- The HPN is 4km x 4km extrapolation of either HPE or Bias HPE, created every 5 min using its own feature-tracking algorithm.
- HPN is designed to provide FFMP with 1hr QPF to generate lead time in flash flood decision making.
- Output is 15-min rain rate forecasts (at 15, 30, 45, and 60 min) and a 1-hour precip accumulation (default 1-hr forecast).
- HPN is designed to be viewable as a separate product in the Volume Browser and is displayable inside FFMP. In the FFMP Basin Table, the HPN is enabled from the Attributes button, and it will create a “split window” duration with a fixed 1hr accumulation of QPF that is added to QPE to provide precipitation accumulations valid for 1hr from now (e.g. “split window” accumulations for 3hr in FFMP Table slider bar will be 2hrs QPE + 1hr QPF; see Figure 7 for example of 0hr QPE and 1hr QPF).
- What is the Multi-Sensor Precipitation Estimator (MPE)?
- MPE is a suite of software designed for hydro focal points to combine radar data and rain gauges to create better precipitation estimates. MPE is used at RFCs and at some WFOs to create the bias factors used in Bias HPE as well as other precipitation-related products.
- The MPE perspective is loaded from the “Open Perspectives” button in CAVE.
- What is a mean-field bias?
- MPE calculates a single mean-field bias (e.g. 1.25) for a radar’s precip source by identifying positive accumulations from the radar bins and gauges, only at the location of the gauges. The algorithm sums all gauge accumulations and divides by the radar estimates at the gauge locations. The bias factor is multiplied by the original precip accumulation in order to adjust the precipitation estimate for the current hour. The bias factor for the current hour is not applied to previous hours.
- For instances where the bias changes throughout the radar domain due to melting layer or environmental differences, the mean-field bias will not perform similarly across the domain. The local bias can perform better in these circumstances if there are sufficient gauge observations.
- What is the site-local bias?
- Instead of creating one single bias (mean-field), a spatially varying bias field is created using all available gauges within 40 km of every fourth grid point. To create a local bias, there needs to be 10 gauge-pair observations. To achieve this threshold, the time window is expanded until this condition is met (just like the mean-field bias). The bias values are then linearly interpolated between grid points.
- How often does the bias factor update?
- The bias factors typically update around 25 min after the hour. MPE at the RFCs or at the local WFO is set up to continuously calculate the biases and make it available to FFMP on an hourly basis.
- What time window does MPE use to calculate the mean-field bias?
- MPE is supposed to use 10 radar-gauge pairs to calculate mean-field biases. It first looks in the current hour, and if there are not enough gauge-radar pairs of measurable precipitation, then it increases the search window using the latest 2hrs, 3hrs, 5hrs, 10hrs, 1week, 1month, 3 months, and 1142yrs (i.e. lifetime). If the gauge pairs are being reported less than 10, then this is likely broken in MPE (has been routinely observed). If it is early in an event following a long dry spell and MPE is functioning properly, then it is possible for the biases to be from a long time ago and might not be representative.
- What is the FFMP Virtual Gauge Basin (VGB)?
- FFMP calculates precip accumulations at gauge locations in a unique way, so you can compare the point-based gauge value with a raw radar point-based value, as opposed to the areal averages applied with basin, county, or HUC-level aggregates. At every gauge location, FFMP accumulates precipitation using the nearest raw input data point. This can be the nearest low-altitude radar bin for a DHR or DPR source, or it can be the nearest gridpoint in the 1km resolution gridded HPE or Bias HPE data. The VGB location in the D2D FFMP display is annotated by white boxes at certain zoom levels, and in the FFMP table, all VGB cell names are colored purple.
- How do I compare a VGB to a gauge value in FFMP?
- When you right-click on a basin name in the FFMP table, you launch a basin trend. If you check the "gauge" box in the Plots section in the upper right, you turn on the gauge overlay. The light-blue line is the gauge value (reported hourly) and the radar QPE is the black line (reported every 3-5 minutes).
For questions or comments about HPE and Bias HPE or bias information in AWIPS, please contact Michael Magsig or Jill Hardy at WDTD.