# Presentation: 666442

## Data Windowing in ORDATechnical Briefing

- Sebastián Torres1,2, Chris Curtis1,2,Rodger Brown2, and Michael Jain2
- 1Cooperative Institute for Mesoscale Meteorological Studies 2National Severe Storms Laboratory

**NEXRAD **
**Technical Advisory Committee Meeting**
- March 27, 2007

## What is Data Windowing?

**What is Data Windowing?**

- Unlike legacy RDA, ORDA uses **data** windows
- Time-series samples used to compute base data moments are **weighted** using a “window”
- Data windows available in ORDA are:
- rectangular (no window)
**Equivalent to legacy RDA**
- Hamming
- von Hann
- Blackman

- More aggressive

## Why Data Windowing?

- Tapered data windows are usually applied before processing in the frequency domain (spectral processing)
- Aggressive windows have lower frequency sidelobes that help reduce the frequency “leakage” effect
*In ORDA*: GMAP, SZ-2
- Tapered data windows reduce the effective antenna beamwidth due to scanning
- A narrower effective beamwidth results in smaller resolution volumes
*In ORDA*: Super Resolution

## The Effects of Data Windowing

*Tapered* windows reduce the equivalent number of independent samples available to estimate spectral moments
- End samples “contribute less” to the estimation process
- The more **aggressive** the data window, the larger the **errors** of estimates for _all base data moments_

**Rectangular**
**Window**

**Hamming**
**Window**

## Standard Error of Moment Estimates for Different Windows vs. Spectrum Width (VCP 11)

**Standard Error of Moment Estimates for Different Windows vs. Spectrum Width (VCP 11)**

**Parameters correspond to 1****st**** split cut of VCP 11**

*M* = 17, *T**s* = 3.1 ms, SNR = 10 dB

*M* = 52, *T**s* = 1 ms, SNR = 10 dB

## Standard Error of Moment Estimates for Different Windows vs. SNR (VCP 11)

**Standard Error of Moment Estimates for Different Windows vs. SNR (VCP 11)**

**Parameters correspond to 1****st**** split cut of VCP 11**

*M* = 17, *T**s* = 3.1 ms, ***v* = 4 m/s

*M* = 52, *T**s* = 1 ms, ***v* = 4 m/s

## Standard Error of Moment Estimates for Different Windows vs. SNR (VCP 12)

**Standard Error of Moment Estimates for Different Windows vs. SNR (VCP 12)**

**Parameters correspond to 1****st**** split cut of VCP 12**

*M* = 15, *T**s* = 3.1 ms, ***v* = 4 m/s

*M* = 40, *T**s* = 1 ms, ***v* = 4 m/s

## Relative Error Increase for Different Data Windows

- Compared to using a rectangular data window (no window), use of tapered data windows results in **higher standard deviation of **_**all**_** base data moments**
- For ***v* = 4 m/s and high SNR
- The **Hamming** window increases the errors by about **30%**
- The **von Hann** window increases the errors by about **35%**
- The **Blackman** window increases the errors by about **50%**

## A Timeline of Data Windowing in the RDA

**A Timeline of Data Windowing ****in the RDA**

**Past** (before ORDA)
- Rectangular: all legacy RDA algorithms
**Present** (ORDA Builds 8 and 9)
- Hamming: default window
- Blackman: GMAP ground clutter filter
- von Hann: SZ-2 with overlaid echoes
**Near Future** (ORDA Builds 10 through 12)
- Rectangular: *proposed* default window
- Blackman: GMAP ground clutter filter
- von Hann: SZ-2 with overlaid echoes and Super-Resolution
**Future** (ORDA Build 13 and beyond)
- Same as Build 12 plus...
- von Hann: spectral processing?
- Windowing would not be necessary in case of unimodal spectra

*How does the ****present**** system deviates from the ****past****?*
- Compare performance of **Rectangular** vs. **Hamming**

## VCP 11 Comparison

|  |  | Surveillance |  | Doppler |  | Rectangular window |  |  |  | Hamming window |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Elv (deg) | WF | PRI | M | PRI  | M | SD(Z) (dB)* |  | SD(v) (m/s) | SD(w) (m/s) | SD(Z) (dB)* |  | SD(v) (m/s) | SD(w) (m/s) |
| 0.5 | CS | 1 | 17 |  |  | 0.59 |  | - | - | 0.80 |  | - | - |
| 0.5 | CD |  |  | 5 | 52 | - |  | 0.89 | 0.73 | - |  | 1.20 | 0.89 |
| 1.45 | CS | 1 | 16 |  |  | 0.61 |  | - | - | 0.83 |  | - | - |
| 1.45 | CD |  |  | 5 | 52 | - |  | 0.89 | 0.73 | - |  | 1.20 | 0.89 |
| 2.4 | B | 1 | 6 | 5 | 41 | 0.94 | 0.63 | 1.01 | 0.86 | 1.31 | 0.84 | 1.34 | 1.04 |
| 3.35 | B | 2 | 6 | 5 | 41 | 1.04 | 0.63 | 1.01 | 0.86 | 1.42 | 0.84 | 1.34 | 1.04 |
| 4.3 | B | 2 | 6 | 5 | 41 | 1.04 | 0.63 | 1.01 | 0.86 | 1.42 | 0.84 | 1.34 | 1.04 |
| 5.25 | B | 3 | 10 | 5 | 41 | 0.97 | 0.63 | 1.01 | 0.86 | 1.29 | 0.84 | 1.34 | 1.04 |
| 6.2 | B | 3 | 10 | 5 | 41 | 0.97 | 0.63 | 1.01 | 0.86 | 1.29 | 0.84 | 1.34 | 1.04 |
| 7.5 | CD |  |  | 6 | 43 | 0.63 |  | 1.01 | 0.92 | 0.84 |  | 1.34 | 1.11 |
| 8.7 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 | 0.85 |  | 1.34 | 1.18 |
| 10 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 | 0.85 |  | 1.34 | 1.18 |
| 12 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 | 0.85 |  | 1.34 | 1.18 |
| 14 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 | 0.85 |  | 1.34 | 1.18 |
| 16.7 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 | 0.85 |  | 1.34 | 1.18 |
| 19.5 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 | 0.85 |  | 1.34 | 1.18 |

*f* = 2800 MHz, PRI Delta C

- * Reflectivity errors in the Batch mode are indicated for overlaid / non-overlaid situations.

|  |  | Surveillance |  | Doppler |  | Rectangular window |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Elv (deg) | WF | PRI | M | PRI  | M | SD(Z) (dB)* |  | SD(v) (m/s) | SD(w) (m/s) |  |
| 0.5 | CS | 1 | 17 |  |  | 0.59 |  | - | - |  |
| 0.5 | CD |  |  | 5 | 52 | - |  | 0.89 | 0.73 |  |
| 1.45 | CS | 1 | 16 |  |  | 0.61 |  | - | - |  |
| 1.45 | CD |  |  | 5 | 52 | - |  | 0.89 | 0.73 |  |
| 2.4 | B | 1 | 6 | 5 | 41 | 0.94 | 0.63 | 1.01 | 0.86 |  |
| 3.35 | B | 2 | 6 | 5 | 41 | 1.04 | 0.63 | 1.01 | 0.86 |  |
| 4.3 | B | 2 | 6 | 5 | 41 | 1.04 | 0.63 | 1.01 | 0.86 |  |
| 5.25 | B | 3 | 10 | 5 | 41 | 0.97 | 0.63 | 1.01 | 0.86 |  |
| 6.2 | B | 3 | 10 | 5 | 41 | 0.97 | 0.63 | 1.01 | 0.86 |  |
| 7.5 | CD |  |  | 6 | 43 | 0.63 |  | 1.01 | 0.92 |  |
| 8.7 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 |  |
| 10 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 |  |
| 12 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 |  |
| 14 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 |  |
| 16.7 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 |  |
| 19.5 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 |  |

|  |  | Surveillance |  | Doppler |  | Rectangular window |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Elv (deg) | WF | PRI | M | PRI  | M | SD(Z) (dB)* |  | SD(v) (m/s) | SD(w) (m/s) |  |
| 0.5 | CS | 1 | 17 |  |  | 0.59 |  | - | - |  |
| 0.5 | CD |  |  | 5 | 52 | - |  | 0.89 | 0.73 |  |
| 1.45 | CS | 1 | 16 |  |  | 0.61 |  | - | - |  |
| 1.45 | CD |  |  | 5 | 52 | - |  | 0.89 | 0.73 |  |
| 2.4 | B | 1 | 6 | 5 | 41 | 0.94 | 0.63 | 1.01 | 0.86 |  |
| 3.35 | B | 2 | 6 | 5 | 41 | 1.04 | 0.63 | 1.01 | 0.86 |  |
| 4.3 | B | 2 | 6 | 5 | 41 | 1.04 | 0.63 | 1.01 | 0.86 |  |
| 5.25 | B | 3 | 10 | 5 | 41 | 0.97 | 0.63 | 1.01 | 0.86 |  |
| 6.2 | B | 3 | 10 | 5 | 41 | 0.97 | 0.63 | 1.01 | 0.86 |  |
| 7.5 | CD |  |  | 6 | 43 | 0.63 |  | 1.01 | 0.92 |  |
| 8.7 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 |  |
| 10 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 |  |
| 12 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 |  |
| 14 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 |  |
| 16.7 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 |  |
| 19.5 | CD |  |  | 7 | 46 | 0.63 |  | 1.01 | 0.98 |  |

## NEXRAD Requirements and Historical Data Quality

- Meeting NEXRAD data quality requirements
- Requirements formulated to ensure DQ is maintained within the system
- Committee established to assess NTR related to base data quality
- Matching legacy RDA performance
- Algorithms and users were accustomed to data with a certain quality
- Frequently, legacy RDA exceeded requirements
- Data quality of **ORDA compared to legacy RDA** determines the “*DQ Delta*” that users and algorithms are experiencing
- Currently evaluating the operational impact of using a tapered data window all the time (“apples-to-apples” comparison)
- Impact may be worse for
- FAA’s fully-automated algorithms
- Data assimilation into numerical forecast models
**Polarimetric variables**

## Base Data ComparisonReflectivity (KCRI – 03/19/2006)

## Base Data ComparisonReflectivity (KCRI – 03/19/2006)

**Rectangular**
- window

## Base Data ComparisonReflectivity (KCRI – 03/19/2006)

**Hamming**
- window

## Algorithm Performance ComparisonOne-hour Precipitation Accumulation

- window

**Algorithm Performance Comparison****One-hour Precipitation Accumulation**

- Courtesy Bob Lee (ROC)

## Algorithm Performance ComparisonOne-hour Precipitation Accumulation

- window

**Algorithm Performance Comparison****One-hour Precipitation Accumulation**

- Courtesy Bob Lee (ROC)

## Algorithm Performance ComparisonMesocyclone Detection Algorithm

- time

- Accumulated number of detections

## Near-Future Impact of Changing the Default Data Window in ORDA

|  |  |  | Range Gates with ... |  |  |
| --- | --- | --- | --- | --- | --- |
|  |  |  | Clutter | Overlaid echoes | Clean echoes |
| Split Cuts | Surveillancedata | Baseline processing |  |  |  |
|  |  | Super Resolution |  |  |  |
|  | Doppler data | Baseline processing |  |  |  |
|  |  | Super Resolution |  |  |  |
|  |  | SZ-2 |  |  |  |
| Batch Cuts |  | Baseline processing for Long-PRT data |  |  |  |
|  |  | Baseline processing for Short-PRT data |  |  |  |
| Doppler Cuts |  | Baseline processing |  |  |  |

|  |  |  | Range Gates with ... |  |  |
| --- | --- | --- | --- | --- | --- |
|  |  |  | Clutter | Overlaid echoes | Clean echoes |
| Split Cuts | Surveillancedata | Baseline processing | Blackman | - | Default |
|  |  | Super Resolution | Blackman | - | Von Hann |
|  | Doppler data | Baseline processing | Blackman | Default | Default |
|  |  | Super Resolution | Blackman | Von Hann | Von Hann |
|  |  | SZ-2 | Blackman | Von Hann | Default |
| Batch Cuts |  | Baseline processing for Long-PRT data | Rectangular | - | Rectangular |
|  |  | Baseline processing for Short-PRT data | Blackman | Default | Default |
| Doppler Cuts |  | Baseline processing | Blackman | - | Default |

|  |  |  | Range Gates with ... |  |  |
| --- | --- | --- | --- | --- | --- |
|  |  |  | Clutter | Overlaid echoes | Clean echoes |
| Split Cuts | Surveillancedata | Baseline processing | Blackman | - | Hamming |
|  |  | Super Resolution | Blackman | - | Von Hann |
|  | Doppler data | Baseline processing | Blackman | Hamming | Hamming |
|  |  | Super Resolution | Blackman | Von Hann | Von Hann |
|  |  | SZ-2 | Blackman | Von Hann | Hamming |
| Batch Cuts |  | Baseline processing for Long-PRT data | Rectangular | - | Rectangular |
|  |  | Baseline processing for Short-PRT data | Blackman | Hamming | Hamming |
| Doppler Cuts |  | Baseline processing | Blackman | - | Hamming |

|  |  |  | Range Gates with ... |  |  |
| --- | --- | --- | --- | --- | --- |
|  |  |  | Clutter | Overlaid echoes | Clean echoes |
| Split Cuts | Surveillancedata | Baseline processing | Blackman | - | Rectangular |
|  |  | Super Resolution | Blackman | - | Von Hann |
|  | Dopplerdata | Baseline processing | Blackman | Rectangular | Rectangular |
|  |  | Super Resolution | Blackman | Von Hann | Von Hann |
|  |  | SZ-2 | Blackman | Von Hann | Rectangular |
| Batch Cuts |  | Baseline processing for Long-PRT data | Rectangular | - | Rectangular |
|  |  | Baseline processing for Short-PRT data | Blackman | Rectangular | Rectangular |
| Doppler Cuts |  | Baseline processing | Blackman | - | Rectangular |

**Near-Future Impact of Changing the ****Default Data Window in ORDA**

## Conclusions

**Hamming window** increases errors of _all_ base data moments
- Compared to legacy RDA current data has ~**30% larger errors**
- VCPs that met NEXRAD DQ technical requirements with legacy RDA no longer meet them with ORDA
- Is this lower data quality _operationally acceptable_?
- Working on “apples-to-apples” quantitative analyses
- Preliminary results indicate there can be performance differences in certain products
- Users always demand **better data quality** and faster updates
- Back in 2003, one of the TAC’s recommendations was to...* “Produce the best quality data possible from the WSR-88D throughout the remainder of its service life.”*
- e.g., recommendation for super resolution followed this criterion (recombination)

## Recommendations

**Recommendations**

**ORDA should operate with a** **rectangular window** whenever possible
- Making this change is straightforward, low-cost, and would not change the computational complexity of ORDA algorithms
- Historically, requirements have been relaxed only if _significant operational benefits_ were realized
- Clutter filtering → Uncontaminated data
- VCP 12 → Faster updates
- SZ-2 → Recovery of overlaid echoes (reduced obscuration)
- Super Resolution → Improved detection of weather features
- Operating with the Hamming window _does not_ bring any significant operational benefits
- However, before using the rectangular window as the default window, **we recommend** **the ORDA spectrum width estimator be fixed**

## Back-Up Slides

## Relative Standard Error of Moment Estimates for Different Windows vs. Spectrum Width

**Parameters correspond to 1****st**** split cut of VCP 11**

*M* = 17, *T**s* = 3.1 ms, SNR = 10 dB

*M* = 52, *T**s* = 1 ms, SNR = 10 dB

## Relative Standard Error of Moment Estimates for Different Windows vs. SNR

**Relative Standard Error of Moment Estimates for Different Windows vs. SNR**

**Parameters correspond to 1****st**** split cut of VCP 11**

*M* = 17, *T**s* = 3.1 ms, ***v* = 4 m/s

*M* = 52, *T**s* = 1 ms, ***v* = 4 m/s

## Errors with Different Data Windows for VCPs 11, 12, and 21

| VCP 11 | SD(Z) (dB) | SD(v) (m/s) | SD(v) (m/s) |
| --- | --- | --- | --- |
| Rectangular | 0.58 | 0.89 | 0.73 |
| Hamming | 0.80 | 1.19 | 0.90 |
| Von Hann | 0.78 | 1.21 | 0.91 |
| Blackman | 0.89 | 1.35 | 1.05 |

| VCP 12 | SD(Z) (dB) | SD(v) (m/s) | SD(v) (m/s) |
| --- | --- | --- | --- |
| Rectangular | 0.62 | 1.02 | 0.88 |
| Hamming | 0.84 | 1.36 | 1.06 |
| Von Hann | 0.82 | 1.37 | 1.08 |
| Blackman | 0.94 | 1.54 | 1.25 |

| VCP 21 | SD(Z) (dB) | SD(v) (m/s) | SD(v) (m/s) |
| --- | --- | --- | --- |
| Rectangular | 0.46 | 0.68 | 0.52 |
| Hamming | 0.62 | 0.91 | 0.66 |
| Von Hann | 0.62 | 0.93 | 0.68 |
| Blackman | 0.70 | 1.03 | 0.76 |

- Errors correspond to the 1st elevation angle
- For *Z* and ***v*: ***v* = 4 m/s and SNR = 10 dB
- For *v*: ***v* = 4 m/s and SNR = 8 dB

## Relative Errors with Different Data Windows for VCPs 11, 12, and 21

| VCP 11 | SD(Z) SD(Zrect)
SD(Zrect) | SD(v)  SD(vrect)
SD(vrect) | SD(v)  SD(v rect)
SD(v rect) |
| --- | --- | --- | --- |
| Hamming | 38% | 34% | 23% |
| Von Hann | 34% | 36% | 25% |
| Blackman | 53% | 52% | 44% |

- Errors correspond to the 1st elevation angle
- For *Z* and ***v*: ***v* = 4 m/s and SNR = 10 dB
- For *v*: ***v* = 4 m/s and SNR = 8 dB

| VCP 12 | SD(Z) SD(Zrect)
SD(Zrect) | SD(v)  SD(vrect)
SD(vrect) | SD(v)  SD(v rect)
SD(v rect) |
| --- | --- | --- | --- |
| Hamming | 35% | 33% | 20% |
| Von Hann | 32% | 34% | 23% |
| Blackman | 52% | 51% | 42% |

| VCP 21 | SD(Z) SD(Zrect)
SD(Zrect) | SD(v)  SD(vrect)
SD(vrect) | SD(v)  SD(v rect)
SD(v rect) |
| --- | --- | --- | --- |
| Hamming | 35% | 34% | 27% |
| Von Hann | 35% | 37% | 31% |
| Blackman | 52% | 51% | 46% |