Joe Munchak on the science, technology, and data products powering a new generation of global weather observations

Microwave sounders have quietly become one of the most important tools in modern weather forecasting.

These instruments provide critical temperature and humidity observations that feed global numerical weather prediction models, helping meteorologists understand atmospheric conditions across oceans, remote regions, and storm systems where traditional observations are limited.

In a recent webinar on Tomorrow.io’s Microwave Sounder Constellation, Joe Munchak, Vice President of Mission Science at Tomorrow.io, provided a deep technical look into the company’s satellite architecture, instrument performance, and operational data products.

His presentation highlighted how Tomorrow.io’s constellation is expanding the global observing system with rapid-refresh microwave observations designed for operational forecasting, data assimilation, and real-time weather analysis.

What Is the Tomorrow Microwave Sounder?

Joe began by introducing the Tomorrow Microwave Sounder (TMS), a 6U CubeSat microwave sounder derived from NASA-funded TROPICS mission technology.

The original TROPICS instruments were 3U CubeSats designed for rapid-refresh tropical cyclone monitoring. Tomorrow.io expanded that architecture into a larger 6U platform, creating additional room for:

• Enhanced calibration targets
• Improved receiver electronics
• More stable temperature measurements
• Higher overall measurement accuracy

To date, Tomorrow.io has launched 11 TMS satellites, with additional constellation expansion planned.

The mission science team is responsible for generating satellite data products while ensuring both high accuracy and low latency across the processing pipeline.

How Microwave Sounders See Through Clouds

Joe spent significant time explaining what makes microwave sounders fundamentally different from traditional weather satellites.

Most weather satellites operate in the visible and infrared portions of the electromagnetic spectrum. These systems are excellent for observing cloud patterns, cloud-top temperatures, and large-scale atmospheric features.

Microwave sounders operate at much longer wavelengths.

Because those wavelengths are too large to strongly interact with small cloud particles, microwave observations can penetrate through clouds and observe atmospheric structures beneath them.

This allows TMS to:

• Measure atmospheric temperature profiles
• Retrieve humidity information
• Detect precipitation cores inside storms
• Observe water vapor beneath cloud layers
• Sense surface conditions through many cloud systems

Joe demonstrated how microwave imagery reveals features that visible and infrared imagery cannot fully capture, including precipitation structures embedded within convection and moisture patterns hidden beneath cloud cover.

TMS includes 12 channels specifically designed to sample temperature and humidity at different vertical levels throughout the atmosphere.

Building a Rapid-Refresh Global Constellation

The TMS constellation currently consists of 11 satellites deployed across six orbital planes.

According to Joe, this architecture was intentionally designed to maximize revisit rates and reduce observational gaps that exist within traditional microwave sounding systems.

Historically, most operational microwave sounders have operated in a small number of sun-synchronous orbits, meaning satellites pass over locations at roughly the same local times each day.

Tomorrow.io supplements those traditional orbital planes with inclined orbits that shift over time, helping distribute observations more evenly throughout the day.

The result is approximately hourly average global revisit rates, with even more frequent coverage at some latitudes.

Joe emphasized that TMS was never designed to replace government-operated weather satellites. Instead, the constellation was built to complement backbone systems such as:

• NOAA’s ATMS instruments
• EUMETSAT’s MetOp series
• NASA research missions
• JAXA microwave instruments

When combined with these systems, TMS helps fill major temporal gaps in the global observing network.

Validating Instrument Performance

Coverage alone is not enough — data quality is critical.

Joe explained that the mission science team performs extensive calibration and validation efforts to ensure TMS observations meet operational standards.

One key metric is Noise Equivalent Delta Temperature (NEDT), which measures instrument noise and pixel-to-pixel variability.

To validate observations, Tomorrow.io compares TMS measurements against:

• ERA5 atmospheric reanalysis
• NOAA’s Advanced Technology Microwave Sounder (ATMS)
• NASA’s GPM Microwave Imager (GMI)
• Radio occultation temperature profiles

One important finding from these studies is that TMS observations often agree more closely with other satellite instruments than with atmospheric reanalysis systems, suggesting that TMS is capturing atmospheric information not fully represented in current models.

Joe also highlighted independent evaluations conducted by external researchers, including comparisons performed by Professor Mitch Goldberg at the City College of New York.

Those studies found that while larger instruments like ATMS still outperform TMS in some areas due to lower instrument noise and additional channels, TMS compares favorably with newer-generation microwave sounder systems currently under development.

Delivering Operational Data Products

Joe then shifted into the constellation’s operational data products.

Tomorrow.io generates a full suite of Level 1 and Level 2 products through automated cloud-native processing pipelines powered by Argo Workflows and Kubernetes infrastructure.

Data products are typically delivered within approximately 10 minutes of receiving raw satellite downlinks.

Available products include:

• Native brightness temperature observations
• Resampled geolocated products
• Intercalibrated brightness temperatures
• Limb-adjusted imagery
• Temperature and humidity retrievals
• Cloud and precipitation parameters
• Storm-top height estimates

The company also produces Level 3 gridded Zarr datasets optimized for cloud-native workflows and large-scale analytics.

According to Joe, these products support a wide range of applications, including:

• Numerical weather prediction
• Data assimilation
• Machine learning workflows
• Convective storm monitoring
• Short-term atmospheric change detection

One particularly important capability enabled by the constellation is rapid time-difference analysis between observations, allowing scientists to monitor convective growth and decay at timescales that were previously difficult with traditional microwave systems.

Expanding the Global Observing System

Joe’s presentation illustrated how Tomorrow.io’s Microwave Sounder Constellation is helping expand both the scale and frequency of global atmospheric observations.

By combining rapid-refresh coverage, cloud-penetrating microwave sensing, and operational-grade data products, the constellation is contributing a new layer of weather intelligence to the broader forecasting ecosystem.

As forecasting systems continue evolving toward higher-frequency, data-driven prediction models, rapid-refresh microwave constellations like TMS are positioned to become an increasingly important part of the future global observing system.