DXLook Introduces Real-Time D-RAP Visualization for HF Absorption Events

DXLook has released a new D-RAP (D-Region Absorption Prediction) view that helps amateur radio operators understand and visualize HF absorption caused by solar X-ray flares in real time.

D-region absorption is a major cause of sudden daytime HF blackouts, particularly on lower-frequency bands. DXLook’s new D-RAP view presents existing D-region absorption data in a band-aware, geographic format, allowing operators to visually assess where and on which HF bands absorption may be occurring at a given moment.

The D-RAP view is primarily driven by official data from the NOAA Space Weather Prediction Center, using the global “frequency for 1 dB absorption” product based on GOES satellite X-ray measurements. This dataset identifies, for each region of the Earth, the highest HF frequency expected to experience significant D-layer absorption at the current time.

When NOAA data is unavailable or becomes outdated, DXLook automatically switches to a physics-based fallback model derived from real-time solar position calculations. The system clearly indicates when calculated data is being used instead of measured NOAA data, ensuring transparency for users.

Absorption regions are displayed as smooth, color-coded zones aligned with amateur HF bands, allowing operators to quickly assess which frequencies may be degraded. The D-RAP view integrates with DXLook’s existing MUF, spot, and propagation tools, helping users understand the full operating window between D-layer absorption at lower frequencies and ionospheric refraction limits at higher ones.

The new D-RAP view is especially useful for contest operators, DXers, and emergency communications groups assessing HF reliability during solar events, as well as for operators trying to understand sudden short-wave fadeouts during daylight hours.

The D-RAP view is now live and available to all users at https://dxlook.com.

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About DXLook

DXLook is a real-time HF and VHF propagation visualization platform built by amateur radio operators for the amateur radio community. It combines live reception reports, space weather data, and physics-based modeling to help operators better understand band conditions and propagation behavior worldwide.

 

Wow! Great job DXLook! But remember folks, just because the 'conditions' look bad, and you don't see anyone on your pretty waterfall display doesn't me you should just lurk or turn the radio off. Please get on the air and call CQ! You'll be pleasantly surprised at who and where comes back to you 73

 

Good work. Would you consider adding toggled layers for troposphere related weather? It would augment your APRS layer nicely. Weather fronts, pressure gradients, radar maps with cloud heights, wind maps, etc. Edit added: And aurora maps, too.

 

Very intuitive

 

This is real good information if you work 160 through 40 meters, D affects it so much with the absorption.

73

 

Hi W2EV! I’m always thinking about what else I can add The project actually started with just one view (Summary), and now it includes Summary, Clusters, MUF, D-RAP (the new one), Reports, Real Time, POTA, and QSO. It’s been a huge effort not only to build new features, but also to keep everything running .

Regarding weather, the main issue is the data sources. The good ones are expensive, and for a free project based on donations, that makes it a bit complicated. There is an idea in the backlog to include electrical activity in the band-conditions calculations, but it’s a lot of work, so it won’t happen anytime soon.

That said, stay tuned — I’m constantly tweaking the project, adding new features, and improving things all the time.
73,
Rodrigo - AK6FP

 

I only started using all these DX tools just 10, 12 or so years ago and by then I already had over 300 worked and confirmed.Even back in the 60s,70s, and 80s we had a telephone network and that's how we found out about openings or watched tv channels 2,3,4,and 5 or listened to the 30-50 MHz public service band for the " skip " to come in. Our fire dispatch would very often get covered up by the Greenville Emergency dispatch, Greenville,SC

 

Although closer to true DX HF operating conditions, how is this quantified or resolved when compared to foF2 reported by Ionospheric Map ? (https://www.sws.bom.gov.au/HF_Systems/6/5) Should be noted VOA CAP appears to follow on my probability for reaching another area of the world.

 

Great question! D-RAP and foF2 measure fundamentally different ionospheric phenomena, and they're complementary rather than competing metrics.

foF2 (critical frequency of the F2 layer) tells you the ceiling - the maximum frequency that will refract back to Earth at vertical incidence. It's essentially what makes long-distance HF propagation possible. The ionosonde network you referenced measures this directly.

D-RAP tells you about the floor - the absorption penalty that signals pay when passing through the lower ionosphere (D-layer), especially during solar X-ray events. This affects the lower HF bands most severely (inverse square relationship with frequency).

So the practical operating window is: frequencies above D-layer absorption but below the MUF.

DXLook's MUF View - We also have a separate MUF view that takes a different approach than ionosonde-based predictions. Rather than using foF2 measurements, we derive MUF empirically from actual observed signal paths. For every spot we ingest (from PSK Reporter, RBN, WSPRnet, DX Cluster), we calculate the path midpoint between sender and receiver. We then take the median observed frequency for each geographic cluster and display that as the "working MUF" for that region. This is observational rather than predictive - it shows what frequencies are actually refracting successfully right now, not what theory says should work.

The advantage of this approach is that it's grounded in real propagation; the limitation is that it only shows where active operators happen to be transmitting. Combining our empirical MUF with ionosonde-derived foF2 predictions would give an even more complete picture.

Regarding D-RAP specifically: DXLook's D-RAP view primarily uses NOAA SWPC's official D-RAP product, which provides the "highest frequency experiencing ≥1 dB absorption" at each grid point, driven by real-time GOES X-ray measurements. When NOAA data becomes stale (which unfortunately happens), we fall back to a Chapman-layer model based on solar zenith angle - essentially modeling how D-layer ionization varies with sun position. We're transparent in the UI about which data source is active.

You're right that VOA CAP (and VOACAP/ICEPAC) take a more integrated approach, modeling the full path including both absorption losses and F-layer refraction. DXLook's philosophy is more observational - we show what's actually being heard (via aggregated spots) alongside physics-based overlays (D-RAP, solar terminator), rather than purely predicting what should be heard. Different tools for different purposes!

For a complete picture, using foF2 maps for theoretical MUF + DXLook's empirical MUF for "what's working now" + D-RAP for absorption awareness makes sense. We're always looking to improve - integrating ionosonde foF2 data is something we've considered for future development.

73!
AK6FP

 

Agrees with my s-meter noise floor.
73's Dan

 

THANK YOU FOR YOUR REPLY ! Its one thing to hear, but another to be heard. Your program takes the hype out of another alleged good propagation day (argh) and puts it into perspective what propagation day you really are going to have. I been chasing this basic question of propagation for years researching and reviewing reporting systems quantifying for me best operating frequencies during the 24 hour cycle. Took those results and wrote a research paper, distributed it to various local clubs, and got nothing.

What is somewhat disturbing is without first really understanding "as true to propagation reality as you can get", will cause you to question whether your station, from a systems engineering perspective, is truly functioning properly. FT8 is a useful tool to evaluate real time propagation parametrics (distance, signal strength, etc.)

For me truly understanding my propagation day is important while chasing DX using FT8.

73 !

 

Thank you for taking the time to write this — I really appreciate it.

What you describe resonates strongly with the motivation behind DXLook. Without a realistic view of propagation, it’s very easy to misdiagnose problems and start questioning antennas, power levels, or equipment, when in reality the limiting factor is simply the ionosphere at that moment. That confusion is frustrating, especially for operators who think in engineering terms and want measurable cause-and-effect.

FT8 has been incredibly valuable in this regard. Used at scale, it becomes less about making QSOs and more about acting as a distributed measurement system — showing distance, signal strength, timing, and band-dependent behavior in a way that traditional prediction tools can’t always capture in real time. That observational aspect is what DXLook tries to highlight: not what should work in theory, but what is working right now.

I also appreciate you mentioning the difficulty of getting this kind of thinking adopted. Bridging the gap between theory, prediction, and operational reality has always been challenging in HF, and it’s something many of us have struggled with for years.

Thanks again for the thoughtful discussion and for sharing your perspective. Conversations like this are exactly what help refine these tools and keep them grounded in real operating experience.

73,
Rodrigo – AK6FP

 

I dig it the most!

 

Forgot to add that foF2 is related to ion F2 density and this can change depending upon solar activity giving appearance the foF2 ceiling frequency is a lot higher than reported, something like a MUF map. Also not unusual ion plasma can shift causing an HF signal to pass through the F2 layer out into space, or can enhance refraction. I learned foF2 generally report ceiling frequency and is not an exact science. Sort of like Doppler weather radar with a lower 300 feet height before registering a local storm.