ATTACHMENT_A_Proposers_Day_Material.pdf

Frosty Frank Robey, D.Sc., FIEEE, FMSS

Proposers Information

December 22, 2025

Distribution Statement “A” (Approved for Public Release, Distribution Unlimited)

Frosty: leverage noise-like illumination to provide arctic sensing

Platform images derived from:

https://www.dvidshub.net/image/7966462/coast-guard-cutter-healy-conducts-science-missions-beaufort-sea https://disciplesofflight.com/wp-content/uploads/2015/05/Art_Joe-Erickson-IMG_6257a_SM.jpg

4. Coherent HF Surface wave return path

3. Illumination of targets & receive array

1. Externally energized field

5. Receive/processing

2. Dispersive decorrelating channel

DARPA Graphic

• Assured Arctic Awareness program (2013)

• Experimental program investigated noise illumination

• Deployed single elements for data collection

• Demonstrated basic concept but noise anisotropy and color limited results

• Defense Applications of Innovative Remote Sensing (ongoing)

• Theoretical development with experimental underpinning

• Currently deploying polarimetric arrays for data collection in low latitudes (Kwajalein)

• Low latitude presents different ionospheric challenges from high latitude

• Will provide initial data to Frosty

DARPA Legacy Programs

-500 -400 -300 -200 -100 0 100 200 300 400 500 Delay (us)

-50 -45 -40 -35 -30 -25 -20 -15 -10 -5

Gain with number of elements

124816

Antenna

Clutter

Target

Co rre la tio n (d

B)

DARPA Graphics DARPA Graphics

• Insight: Standoff high-power illumination can provide the detection SNR needed for arctic radar.

• SNR is degraded by auroral scintillation

• Requires complex processing rather than straightforward matched filter

Standoff illumination through decohering propagation path

𝑺𝑺𝑺𝑺𝑺𝑺 =

𝑴𝑴𝑷𝑷𝒕𝒕𝑮𝑮𝒕𝒕𝑵𝑵𝑨𝑨𝒆𝒆𝑻𝑻𝒊𝒊𝒊𝒊𝒊𝒊𝝈𝝈

𝟒𝟒𝟒𝟒 𝟐𝟐𝑹𝑹𝟏𝟏𝟐𝟐𝑹𝑹𝟐𝟐𝟐𝟐𝒌𝒌𝑻𝑻𝒔𝒔𝑳𝑳

Propagation loss: e.g. over surface wave path

Maintaining coherenceCombining sources

High-frequency Active Auroral Research Program

(HAARP)

(Transmitter coordinated thus far, other sources are to be determined)SNR: Signal to noise ratio SuperDARN: Super Dual Auroral Radar Network AFLCMC: Air Force life cycle management center

M: Number of illumination sources 𝑃𝑃𝑡𝑡: Transmit power, 𝐺𝐺𝑡𝑡: transmit gain 𝑁𝑁: Number of receiver antenna elements 𝐴𝐴𝑒𝑒: Effective receive area of each receiver element 𝑇𝑇𝑖𝑖𝑖𝑖𝑖𝑖: Coherent integration time 𝜎𝜎: Target’s radar cross section 𝑅𝑅1: Distance from illuminator to target 𝑅𝑅2: Distance from target to receive antenna 𝑘𝑘: Boltzmann’s constant (1.38E-23) 𝑇𝑇𝑠𝑠: System noise temperature 𝐿𝐿: Additional loss

Graphics used with permission from University of Alaska Fairbanks

• SNR via cross correlation processing can degrade with anisotropic illumination.

• Theoretical equations assumed isotropy

• Anisotropic noise raises the clutter floor via dispersion

• Insight: Phased array or beam antenna can correct geometry-induced dispersion

• Metric: Target probability of detection and detection range

Passive Ambient Noise Radar (PANR) illumination: Incoherence and Anisotropy

𝐒𝐒𝑪𝑪𝑵𝑵𝑵𝑵 =

𝑵𝑵𝟐𝟐𝑨𝑨𝒆𝒆𝑩𝑩𝑩𝑩𝒊𝒊𝒊𝒊𝒊𝒊𝝈𝝈

𝟒𝟒𝟒𝟒𝑹𝑹𝟐𝟐𝑳𝑳

Propagation loss:

e.g. over surface wave path

Maintaining coherence

Isotropic noise illumination model:

𝑟𝑟𝑖𝑖,𝑗𝑗 𝜏𝜏 =

𝐴𝐴𝑒𝑒𝑁𝑁𝑜𝑜

2𝜋𝜋 𝜔𝜔 θ,ϕ 𝑒𝑒𝑗𝑗 𝜔𝜔 𝑐𝑐 𝐬̅𝐬⋅ 𝐬𝐬𝑖𝑖−𝐬𝐬𝑗𝑗 𝑒𝑒𝑗𝑗𝑗𝑗𝑗𝑗 sin𝜙𝜙 𝑑𝑑𝑑𝑑 𝑑𝑑𝑑𝑑 𝑑𝑑𝑑𝑑 𝑟𝑟𝑖𝑖,𝑗𝑗 𝜏𝜏 = 2𝐴𝐴𝑒𝑒𝑁𝑁𝑜𝑜 � 𝜔𝜔 𝑒𝑒𝑗𝑗𝑗𝑗𝑗𝑗 sin𝜔𝜔𝑐𝑐 𝑑𝑑 𝜔𝜔 𝑐𝑐 𝑑𝑑 𝑑𝑑𝑑𝑑

As bandwidth ∞, 𝑟𝑟𝑖𝑖,𝑗𝑗, converges to Green’s function

Reference: F. C. Robey, “A covariance modeling approach to adaptive beamforming and detection,” MIT Lincoln Laboratory Technical Report 918, 30 July 1991. Available via DTIC:

https://apps.dtic.mil/sti/tr/pdf/ADA241887.pdf

-500 -400 -300 -200 -100 0 100 200 300 400 500 Delay (us)

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

Gain with number of elements

Antenna

Clutter

Target

N or m al iz ed c or re la tio n

(d B

SCNR: Signal to clutter plus noise ratio 𝑁𝑁: Number of receiver antenna elements 𝐴𝐴𝑒𝑒: Effective receive area of each receiver element 𝐵𝐵: Integration bandwidth 𝑇𝑇𝑖𝑖𝑖𝑖𝑖𝑖: Coherent integration time 𝜎𝜎: Target’s radar cross section 𝑅𝑅: Distance from target to receive antenna 𝐿𝐿: Additional loss 𝑟𝑟𝑖𝑖,𝑗𝑗(𝜏𝜏): Element to element cross correlation at time 𝜏𝜏 𝑁𝑁0: Noise spatial power spectral density (W/sr/m2) 𝐵𝐵: Integration bandwidth 𝜔𝜔: Radian frequency 𝐬̅𝐬: Vector pointing in source direction 𝐬𝐬𝑖𝑖 , 𝐬𝐬𝑗𝑗: Vector from origin to element 𝑖𝑖 or 𝑗𝑗.

𝑐𝑐: Speed of propagation

DARPA Graphic

• Noise-like illumination currently needs cross-correlation of reference and target beams

• Geometry dependent dispersion degrades correlation

• Dispersion should be correctable by frequency and angle-dependent all-pass => requires array directivity

• Key risks for Frosty are:

• Anisotropic radar illumination over unknown time-varying channel

• Hidden models where incomplete data is observed

• Ability to compensate for geometry-dependent dispersion

Passive Ambient-Noise Radar Challenge

Address the noise characterization and decorrelation risk early through exploratory Phase 1

O

T

Target

Reference

Noise field

O

T

Target

Reference

Noise field

Ph as e (r ad

Relative Azimuth (deg)

Dispersion – frequency-dependent phase shift vs. angle

Ph as e (r ad

Azimuth (deg)

Favorable geometry

Ph as e (r ad

Azimuth (deg)

Unfavorable geometry

0 180

-10 -8 -6 -4 -2 0 2 4 6 8 10

80 85 90 95 100

-500

-400

-300

-200

-100

Frequency

Metric

Phase 1:

NotesTarget detection in the arctic environment

Minimum detection range 75 km Ph1: Over the horizon C-12 (@ 1000 ft)

Probability of detection >90%

Probability of Track Tracking is required

Track Accuracy Accuracy is assessed

Timeliness Off-line Ph1: Not more than 90 seconds of data required to form a track

Metrics: Progression to a defense capability

Q1 FY26 Q2 FY26 Q3 FY26 Q4 FY26 Q1 FY27 Q2 FY27 Q3 FY27 Q4 FY27 Q1 FY28

Schedule

Test support and IV&V

Phase 1: Target detection in arctic environment

Data collection

Gov’t

Signal Processing Development

Initial data collection

Kickoff

Source Selection

Distribution Statement “A” (Approved for Public Release, Distribution Unlimited)

Solicitation release

Source Selection

Abstracts due

Oral presentations due OTA award(s)

QPR 1 QPR 2

(Demo 1)

QPR 3 QPR 4

(Demo 2)

Phase 2 Proposers' Day

QPR 5 Final QPR (Demo 3)

Performer

Data collection

Initial GFI data delivery

QPR: Quarterly Program Review GFI: Government Furnished Information IV&V: Independent Verification and Validation

• Notionally, testing will be in Central/Northern Alaska,

• Primarily Point Barrow (maritime & accessible)

• Poker Flat Research Range (under auroral oval)

• A variety of test targets of opportunity and dedicated events

• Transponder for controlled and known response

• Data collection/test events will include truth information

• GPS, AIS and/or ADS-B recording for position information

• Weather – terrestrial and ionospheric

• Illuminator information

Test events

Commercial Dedicated low-altitude

C-12 or similar

Phase 1 Test targets

Vessel of Opportunity / Transponder host https://www.dvidshub.net/image/1073804/alex-haley-patrolhttps://www.jber.jb.mil/News/News-Articles/Article/771148/https://www.flightaware.com/

Google Earth image DARPA Photo

• DARPA is soliciting proposal for innovative radar signal processing algorithms and analysis approaches to produce new sensing modes in the Arctic environment

• Responses are expected to provide an end-to-end solution from raw data to target tracks

• Abstracts and presentations will be evaluated per the program solicitation

Summary

Contracting

• Please pay attention to due dates in Program Solicitation (PS)-26-03 and all instructions – Read the Program Solicitation (PS).

• Important Dates:

Posting Date: 18 December 2025 Questions Due: 7 January 2026, 5PM Eastern Time Abstracts Due: 30 January 2026, 4PM Eastern Time Oral Presentations Due: By Government request, estimated 4-5 weeks after

Abstract submission

• See Section 3.1.g if your organization has not proposed to DARPA previously and note the lead time on new registrations.

DARPA-PS-26-03

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