MPAR Notional Functional Requirements Document - NOAA

NextGen Surveillance and Weather Radar Capability 

Multifunction Phased Array Radar (MPAR) 

Notional Functional Requirements Document 

Version 1.0 

August 1, 2012

REVISION HISTORY 

Filename Version Approved By Comments Date 

NSWRC NFR Ver1-0.docx 1.0 M. Emanuel Initial Release August 1 2012 

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TABLE OF CONTENTS 

1. Background ........................................................................................................................................... 1 

1.1. Purpose ......................................................................................................................................... 1 

2. Concept ................................................................................................................................................. 1 

2.1. Operational ................................................................................................................................... 1 

2.2. System ........................................................................................................................................... 2 

3. Functional Requirements ...................................................................................................................... 2 

3.1. Terminal Aircraft Surveillance ....................................................................................................... 2 

3.2. Terminal Weather ......................................................................................................................... 6 

3.3. Enterprise Weather ....................................................................................................................... 7 

3.4. En-Route Aircraft Surveillance .................................................................................................... 11 

3.5. Reliability, Maintainability, Availability ....................................................................................... 13 

3.6. System Monitoring and Control .................................................................................................. 13 

3.7. Physical Interfaces ...................................................................................................................... 13 

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1. Background 

The Federal Aviation Administration (FAA) and the National Oceanographic and Atmospheric 

Administration (NOAA) have sponsored studies to evaluate the feasibility of replacing existing primary 

radar systems with phased array radars. The radars under consideration, currently used for aircraft 

surveillance and/or weather sensing, along with their wavelength and band, are: 

• ASR (Airport Surveillance Radar) models 8, 9 and 11 (10 cm, S-band) 

• TDWR (Terminal Doppler Weather Radar) (5 cm, C-band) 

• NEXRAD (Next-Generation Weather Radar) (10 cm, S-band) 

• ARSR (Air Route Surveillance Radar) models 1-4 (30 cm, L-band) 

These radars were developed by different agencies, and deployed at different times in different 

locations for different purposes. Many benefits may be realized if a new radar system(s) could be 

designed to take over the missions of the legacy radars, and reduce the extensive overlapping of those 

legacy radars. Reducing the total number of radars needed for national surveillance, while introducing a 

common radar system design that would simplify logistics and maintenance, has the potential to 

significantly reduce life cycle costs. This can be a realized benefit for the FAA in the terminal domain, 

and across both terminal and en route airspace should a federal enterprise solution be developed. 

1.1. Purpose 

The purpose of this document is to bring forth the MPAR notional functional requirements for each of 

the aircraft and weather surveillance elements currently in place to help drive functional requirements 

for NSWRC. NOTE, in this document where similar requirements are defined with dissimilar values (e.g. 

terminal aircraft surveillance range must be 60nmi / en route aircraft surveillance range must be 

250nmi) the more stringent value will be considered when applicable. 

2. Concept 

2.1. Operational 

The operational concept for a system based on these notional functional requirements would serve 

multiple roles including primary radar aircraft surveillance and terminal weather surveillance for aircraft 

operations specific threats such as gust fronts and microbursts detection. General weather surveillance 

for a variety of tasks, including severe weather detection and warning, hydrology, onset of convection, 

etc, and long range aircraft surveillance to support homeland and national security missions could also 

be included in the operational concept should a federal enterprise acquisition of NSWRC be realized. 

This radar would also deliver wind turbine clutter mitigation, provide Unmanned Aircraft Systems (UAS) 

surveillance, and offer enhanced aircraft target probability of detection and reduced false target 

detection in the terminal domain. 

Operation of radar based on these requirements would be tailored to perform multiple functions, and 

data would be shared among the stakeholders to support all functions. Phased array capability would be 

exploited to adapt scanning strategies to use radar resources to maximum efficiency, minimizing the 

time spent scanning empty space and focusing resources on targets of interest. Data from some scans 

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could be exploited by multiple users to minimize the number of single-user scans consistent with 

meeting the mission requirements of all users. 

2.2. System 

Radar systems deployed based on these requirements would employ a single scalable architecture to 

reduce development, procurement, and logistical costs. Multiple variants, based on aperture size, could 

be mixed to provide the most efficient approach to gathering the required data. For planning purposes, 

two variants have been considered—one for short-range / lower resolution applications and one for 

longer range / high resolution surveillance. However, other possible combinations of variants could be 

considered. 

3. Functional Requirements 

At a minimum, MPAR must provide Terminal aircraft and weather surveillance for an FAA acquisition. 

Should a Federal Enterprise acquisition be realized, MPAR must also provide En-Route aircraft and 

Weather search coverage under conditions of ground clutter, weather, and interference. MPARs of 

different scale may be considered to fulfill FAA’s terminal and weather surveillance, and the Federal 

Enterprise en-route aircraft and weather surveillance requirements. 

3.1. Terminal Aircraft Surveillance 

3.1.1. Detection Envelope 

The envelope of detection for aircraft must be: 

a) Slant range 0.25 to 60 nmi 

b) Azimuth 360 degrees coverage 

c) Altitude to 28,000 feet above MSL 

d) Elevation 0 to 30 degrees 

3.1.2. Target Detection 

The probability of aircraft detection in the clear must be [90] percent or better when the target has a 

RCS of [0.25] m 2 under the following conditions: 

a) Swerling Case 1 

b) Probability of False alarms of 10 -6 

c) Target is at a range of [55] nmi, at the peak of the beam when boresight is normal to the plane 

of the antenna 

d) Target velocity ranges from [25] to [700] knots and maneuvering up to [3.0] g 

e) Target heading ranges from radial to tangential 

Target detections within the 60nmi range must be protected from range aliasing of aircraft targets 

outside this range. 

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3.1.3. Altitude Determination 

The MPAR must produce height measurements on any detected target within the detection envelope 

specified in 3.1.1. The accuracy requirements are as specified in paragraph 3.1.9. 

3.1.4. Range Resolution 

When returns are detected from two Swerling Case 1 targets, separated in range by at least [0.125] nmi, 

on the same azimuth, with the same or different radial velocities, and located at any point in the 

coverage volume, the MPAR must resolve the two targets and generate two unique target reports [80] 

percent of the time for any combination of RCS from [0.25] to [20] m 2 provided that the larger target’s 

RCS is not more than [8] dB greater that the smaller target’s RCS. 

3.1.5. Azimuth Resolution 

When returns are detected from two Swerling Case 1 targets, separated in azimuth by [2.6] degrees, at 

the same range, with the same or different radial velocities and located at any point in the coverage 

volume, the MPAR must resolve the two targets and generate two unique target reports [80] percent of 

the time for any combination of RCS from [0.25] to [20] m 2 provided that the larger target’s RCS is not 

more than [8] dB greater than the smaller target’s RCS. 

3.1.6. Target Split 

The single dwell probability of a split report for MPAR must be less than [0.75] percent for targets having 

a SNR greater than or equal to [20] dB. 

3.1.7. Range Accuracy 

The MPAR must provide single dwell range surveillance information which is accurate to [275] feet RMS 

including all bias and errors, for a target with a median SNR greater than [30] dB, within the entire 

detection envelope in 3.1.1. 

3.1.8. Azimuth Accuracy 

The MPAR must provide single dwell azimuth surveillance information which is accurate to [0.16] 

degrees RMS including all bias and errors, for a target with a median SNR greater than [30] dB, within 

the entire detection envelope in 3.1.1. 

3.1.9. Height Accuracy 

The MPAR must provide single dwell height measurements accurate to [500] ft RMS including all bias 

and errors, of the target’s true altitude. 

3.1.10. Update Rate 

The MPAR must update reports on all aircraft targets within the detection envelope at least once every 

[4.8] seconds, ± 0.5 second. 

3.1.11. Timeliness 

Where the data delay is defined as the time from received signal at the radar antenna until the target 

report is ready for transmission from the MPAR must not exceed [0.16] seconds. 

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3.1.12. Target Outputs 

The MPAR must be capable of outputting for following, on a per scan basis: 

a) [700] aircraft target reports and [300] false target returns, uniformly or non-uniformly 

distributed; 

b) The non-uniform distribution of these targets must be as follows and may occur consecutively in 

any order: 

1. A peak of [250] targets distributed a contiguous 90 degrees of a scan; 

2. A peak of [100] targets uniformly distributed across two contiguous 11.25 degree 

sectors; 

3. A peak of [16] targets in a 1.3 degree wedge lasting for not more than two contiguous 

wedges. 

3.1.12.1. Overload Handling 

Target overload must be handled in a manner that provides both a graceful decrease in target capacity 

and required performance for the remaining targets, based on a defined target priority. 

3.1.13. False Target Processing 

The MPAR must provide false target processing to: 

a) Report no more than [1] false track per minute under normal clutter conditions 

b) Report no more than [10] false tracks per minute when the clutter environment exceeds normal 

conditions. 

c) Report less than [10%] of the total primary radar detections input to the system as false tracks 

under excessive clutter environments. 

3.1.14. Weather Representation 

The MPAR must categorize weather data intensity to the six standard National Weather Service (NWS) 

levels in table 1. 

NWS Level 

NEXRAD Level in Precipitation Mode 

No. Reflectivity (dBZ) No. Reflectivity (dBZ) 

1 ≥ 18 3 

4 

5 

≥15 to

6 ≥ 57 11 

12 

13 

14 

15 

≥55 to

dBsm blade cross section, blade lengths of 44 m, and a maximum rotation rate of 15 rpm. Turbines can 

be spaced as close as 1 nmi from each other within the wind farm area and aircraft are required to fly a 

minimum of 1,000 feet above the highest point within the area. 

3.1.16. Fixed Clutter 

The MPAR must reject non-precipitation clutter (e.g. buildings, mountains etc.). 

3.2. Terminal Weather 

MPAR must detect hazardous weather phenomena to aviation including windshear and gust fronts to be 

conveyed to Air Traffic Control. 

3.2.1. Observation Volume 

There must be full azimuth coverage out to a 60 nautical mile range from the airport reference point 

(ARP) with a height up to 70,000 ft. Observation data (e.g. Doppler velocity) within the 60nmi range 

must be protected from range aliasing of weather signal outside this range. 


There must be an observation volume update every 2.5 minutes and a surface (lowest elevation) 

observation update every 1 minute. 

3.2.3. Spatial Resolution 

a) Range resolution: 150 m. 

b) Azimuthal resolution: 450 m at 6 nautical miles from the ARP. 

c) Vertical resolution: 250 m at 6 nautical miles from the ARP. 

3.2.4. Spatial Accuracy 

a) Range accuracy: 50 m. 

b) Cross-range accuracy: 50 m at 6 nautical miles from the ARP. 

3.2.5. Sensitivity 

The minimum detectable reflectivity must be -20 dBZ at 6 nautical miles from the ARP. 

3.2.6. Radar Outputs Required 

The radar outputs required must be reflectivity, radial velocity, and spectral width. 

3.2.6.1. Reflectivity 

a) Resolution: 1 dBZ. 

b) Accuracy: 2 dBZ (SNR > 10 dB, spectrum width = 1 to 4 m/s). 

3.2.6.2. Radial Velocity 

a) Resolution: 0.1 m/s. 

b) Accuracy: 1 m/s (SNR > 8 dB, spectrum width = 4 m/s). 

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3.2.6.3. Spectrum Width 

a) Resolution: 0.1 m/s. 

b) Accuracy: 1 m/s (SNR > 10 dB, spectrum width 1 to 4 m/s). 

3.2.7. Radial Velocity Range 

There must be a radial velocity measurement range of at least ±40 m/s. 

3.3. Enterprise Weather 

MPAR must have the ability to employ multiple weather scan strategies to scan the complete detection 

envelop periodically for new weather features, characterize those features, and interrogate and track 

them based on their evolution, impact and potential threat. 


The nominal weather detection envelop for a large-aperture variant must be as stated below. Range 

requirements for smaller-aperture variants must be consistent with sensitivity and detection 

requirements. 

a) Range – Reflectivity 1-460km 

b) Range – Doppler 1-300km 

c) Range – Spectrum Width 1-300km 

d) Range- Polarimetric 1-300km 

e) Azimuth 360 degrees coverage 

f) Altitude 70,000 feet above AGL 

g) Elevation -10.0 to 90 degrees 

h) Range Resolution 250 meters 

MPAR must provide weather coverage with no ambiguities to the maximum range 

3.3.2. Maximum Power 

MPAR must have a suitable power aperture to meet weather sensitivity requirements (nominally 0 dB 

SNR for a -4.5 dBZe target at 50km) 

3.3.3. Pulse Length 

MPAR must have suitable power density and pulse lengths to meet resolution requirements and resolve 

weather features in precipitation and clear air. 

3.3.4. Resolution 

MPAR must be able to resolve severe storm features such as mesocyclone and tornadic vortex 

signatures at extended ranges. MPAR must also have the ability to observe phenomena to the top of all 

convective weather and resolve weather features consistent with the type of weather and its associated 

impact. 

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3.3.5. Scanning 

MPAR must have the ability to scan specific areas more rapidly than others while periodically 

performing a full scan of the detection envelop 

3.3.5.1. Volume Scan 

To maintain situational awareness, volume updates for weather evolution must be performed at least 

every 2 minutes over the entire detection envelop 

3.3.5.2. Characterization Scan 

New areas of precipitation and other relevant features must be scanned within 1 minute of a volume 

scan to specifically characterize the nature of the features. 

3.3.5.3. Storm Scan 

Storm-specific scanning strategies must be used for evaluating convective storms. For potentially severe 

convective returns, storm scans must occur every 30 seconds to identify 3D spatial extent, evolution and 

movement, radial wind velocity, reflectivity patterns, hydrometeor type (including hail and hail size), 

severe weather signatures in wind and reflectivity features, and precipitation rate and amount. Nonsevere 

convective returns must be scanned for the same features every 1 minute. Repeated scans must 

track development and movement of features within convective cells, convective cells, and aggregations 

of cells (e.g., thunderstorm lines, multi-cell clusters, etc.). 

3.3.5.4. Clear Air Scan 

MPAR must be capable of detecting and tracking non-hydrometeorological features such as volcanic 

ash, fire plumes and atmospheric discontinuities such as fine lines and outflow boundaries. 

3.3.6. Liquid Water Content 

Liquid water content must be 

a) Updated every minute in stratiform precipitation at .5km horizontal and .1km vertical resolution 

below 5000ft, above 5000ft, resolution will be .5km both horizontally and vertically 

b) Updated every 30 seconds in severe convection at .1km resolution both horizontally and 

vertically 

c) Updated every minute in non-severe convection at .5km horizontal and 100 feet vertical 

resolution below 5000ft, above 5000ft, resolution will be 500 feet both horizontally and 

vertically 

3.3.7. Liquid Water Equivalent 

Liquid water equivalent must be 

a) Detected in a full volumetric scan every 2 minutes 

b) Characterized one time with a minute of detection at 2km horizontal and 1km vertical resolution 

for new targets only 

c) Updated every minute in stratiform precipitation at .5km horizontal and .1km vertical resolution 


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d) Updated every 30 seconds in severe convection at .1km resolution both horizontally and 

vertically 

e) Updated every minute in non-severe convection at .5km horizontal and 100 feet vertical 


vertically 

3.3.8. Median Volume Drop Diameter 

Median volume drop diameter must be 




vertically 



vertically 

3.3.9. Precipitation Type 

Precipitation near the surface and aloft must be 

a) Characterized one time within a minute of detection at 2km horizontal and 1km vertical 

resolution for new targets only 

b) Updated every minute in stratiform precipitation at .5km horizontal and .1km vertical resolution 


c) Updated every 30 seconds in severe convection at .1km resolution both horizontally and 

vertically 

d) Updated every minute in non-severe convection at .5km horizontal and 100 feet vertical 


vertically 

3.3.10. Rainfall Rate and Accumulation 

Rainfall rate and accumulation must be 




vertically 



vertically 

3.3.11. Solid Precipitation Rate and Accumulation 

Solid precipitation (including snow, ice pellets, hail, and other forms of frozen water) rate and 

accumulation must be 

9




vertically 



vertically 

3.3.12. Hail Size 

Hail size must be 

a) Updated every 30 seconds in severe convection at .1km resolution both horizontally and 

vertically 

b) Updated every minute in non-severe convection at .5km horizontal and 100 feet vertical 


vertically 

3.3.13. Winds 

MPAR must be capable of detecting wind speed and direction in both precipitation and clear air 

3.3.13.1.1. Wind Information during Precipitation 

In areas of precipitation wind speed and direction must be 

a) Characterized one time within a minute of precipitation detection at 2km horizontal and 1km 

vertical resolution for new precipitation targets only 

b) Updated every minute in stratiform precipitation at .5km horizontal and .1km vertical resolution 


c) Updated every 30 seconds in severe convection at .1km resolution both horizontally and 

vertically 

d) Updated every minute in non-severe convection at .5km horizontal and 100 feet vertical 


vertically 

3.3.13.1.2. Wind Information in Clear Air 

a. In precipitation free areas, MPAR must be capable of providing wind speed and direction 

information, characterizing the winds to detect possible convective triggers and to create a 

vertical sounding product that shows wind speed and direction at 1000 foot increments to the 

top of the radar’s detection envelop 

b. In areas of expected convection, MPAR must provide updates of wind speed and direction near 

the ground every 30 seconds at .1km resolution both horizontally and vertically 

3.3.14. Cell Movement and Features 

Cell movement and features must be 

10




vertically 



vertically 

3.3.15. Severe Weather Features 

Severe Weather features (e.g., microbursts, large hail, mesocyclones, etc) must be 

a) Characterized one time within a minute of detection at 2km horizontal and 1km vertical 

resolution for new targets only 


vertically 



vertically 

3.4. En-Route Aircraft Surveillance 


The envelop of detection for aircraft must be: 

a) Slant range 1 to 250 nmi 

b) Azimuth 360 degrees coverage 

c) Altitude to 100,000 feet MSL 

d) Elevation -7 to 30 degrees 

3.4.2. Target Detection 

The probability of aircraft detection in the clear must be [80] percent or better when the target has a 

RCS of [2] m 2 under the following conditions: 

a) Swerling Case 1 

b) Probability of False alarms of 10 -6 

c) Target is at a range of [250] nmi, at the peak of the beam when boresight is normal to the plane 

of the antenna. 

d) Target velocity range from [25] to [3000] knots. 

3.4.3. Altitude Determination 

The MPAR must produce height measurements on any detected target within the detection envelope 

specified in 3.4.1. The accuracy requirements are as specified in paragraph 3.4.9. 

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3.4.4. Range Resolution 

When returns are detected form two Swerling Case 1 targets, separated in range by at least [0.125] nmi, 

on the same azimuth, with the same or different radial velocities, and located at any point in the 

coverage volume, the MPAR must resolve the two targets and generate two unique target reports [90] 

percent of the time for RCS of [10] m 2 , between [5] and [250] nmi. 

3.4.5. Azimuth Resolution 

When returns are detected from two Swerling Case 1 targets, separated in azimuth by [2] degrees, at 

the same range, with the same or different radial velocities and located at any point in the coverage 

volume, the MPAR must resolve the two targets and generate two unique target reports [90] percent of 

the time for RCS of [10] m 2 , between [5] and [250]. 

3.4.6. Target Split 

The single dwell probability of a split report must be less than [1] percent. 

3.4.7. Range Accuracy 

The MPAR must provide single dwell range surveillance information which is accurate to [0.125] nmi 

RMS including all bias and errors, within the entire detection envelope in 3.4.1. 

3.4.8. Azimuth Accuracy 

The MPAR must provide single dwell azimuth surveillance information which is accurate to [0.176] 

degrees RMS including all bias and errors, within the entire detection envelope in 3.4.1. 

3.4.9. Height Accuracy 

The MPAR must provide single dwell height measurements accurate to [1000] ft RMS including all bias 

and errors, of the target’s true altitude. 


The MPAR must update reports on all aircraft targets within the detection envelope at least once every 

[12] seconds ± [0.1] seconds. 

3.4.11. Timeliness 

Where the data delay is defined as the time from received signal at the radar antenna until the target 

report is ready for transmission from the MPAR must not exceed [0.35] seconds. 

3.4.12. Target Outputs 

The MPAR must be capable of outputting for following, on a per update interval basis: 

a) [800] aircraft targets and [194] false target returns 

b) The non-uniform distribution of these targets must be as follows and may occur consecutively in 

any order for conditions 1 and 2: 

1. A peak of [50] targets in each of 8 contiguous 11.25 degrees sectors; 

2. A peak of [20] targets in each of 3 contiguous 1.2 degree sectors; 

3. [60] aircraft returns aligned in an azimuth radial (could be at one elevation angle) 

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4. [4] aircraft returns within [4.5] nmi, not necessarily uniformly distributed. 

3.4.12.1. Overload Handling 

Target overload must be handled in a manner that provides both a graceful decrease in target capacity 

and required performance for the remaining targets, based on a defined target priority. 

3.5. Reliability, Maintainability, Availability 

The MPAR must meet or exceed the following reliability, maintainability, and availability requirements: 

a) A minimum inherent system availability value of 0.99999 

b) A system mean time between preventative maintenance actions of 2190 hours; 

c) A mean time between critical failures (MTBCF) of 500 hours, based on an inherent availability of 

0.99999 and an MTTR of 0.5hours; 

d) A system mean time to repair (MTTR) not more than 0.5 hours; 

e) A system mean time to restore (MTR) not more than 1.0 hours 

f) The failure of any LRU must not affect the performance of any other LRU 

3.6. System Monitoring and Control 

Operators such as Air Traffic Controllers and NWS forecasters must have the ability to control the 

operation of MPAR. 

The MPAR must provide for both local and remote maintenance as follows: 

a) On-line performance monitoring to isolate problems to the LRUs; 

b) Local operational control and monitoring through on-line performance monitoring diagnostics 

and off-line fault isolation diagnostics; 

c) Identical control panels and associated software at all ATC sites (radar site, Terminal Radar 

Approach Control (TRACON), and ATC tower). 

d) Provide interface for remote control of radar functions needed to perform fault isolation and 

control from a remote maintenance facility via a maintenance data terminal 

3.7. Physical Interfaces 

3.7.1. Air Traffic Control 

3.7.1.1. Automation Systems 

MPAR must provide interface for dissemination of formatted data to ATC automation systems. 

3.7.1.2. Remote Maintenance and Monitoring 

MPAR must provide interface for remote monitoring of control functions and critical performance data 

MPAR maintenance data must be transmitted and received by remote maintenance and monitoring 

systems. 

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3.7.1.3. Terminal Weather 

MPAR windshear and gust front products must be transmitted and received by weather decision 

support tools. 

3.7.2. National Weather Service 

3.7.2.1. Forecast Offices 

MPAR data must be transmitted to the appropriate NWS Forecast Office. This data must be capable of 

being run through various weather algorithms and formatted for display. 

3.7.2.2. Radar Operations Center 

MPAR data must be transmitted and received by the Radar Operations Center. 

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