PACE Clouds Challenge

Challenge Dates: 15 September – 1 November 2026

Scientists working on NASA’s PACE satellite mission are asking for your help to collect Clouds observations when the PACE satellite is passing over your location.

PACE atmosphere scientist, Dr. Andy Sayer, is interested in comparing your ground-based observations of clouds to PACE data to evaluate how well PACE measures cloud edges and total cloud cover. Sayer is specifically looking for GLOBE Clouds observations taken within a 5-minute window of PACE passing overhead during the PACE Clouds Challenge.

Learn more about PACE and the challenge from the August 2026 GO Connect recording: Meet PACE. 

How You Can Help

Take a Clouds observation when PACE is over your location, within the 5-minute optimal observation window. Timing is critical!

  • Check when PACE will pass over your location. Set the PACE overpass alert in the GLOBE Observer app or look up your location’s times on the NASA GLOBE Satellite Overpass Times page. The app’s alert is sent 15 minutes before an overpass.
  • Be outside and ready 5 minutes before the PACE overpass. Open the Clouds tool only when you are outside and within the 5-minute observation window. The observation timestamp is recorded when you tap New Cloud Observation. 
  • Complete the observation with all six photos. Starting within 5 minutes of the overpass helps place your photos in the optimal observation window. Be sure to include the photo looking straight up at the satellite! Please do not take Clouds observations at night.
  • Submit your observation.

Go Above and Beyond:

  • Tell us what type of phone or device you are using (e.g., iPhone 13 Pro, Samsung Galaxy S26) in the Field Notes section found right below the Feature Photos options. This information will help Sayer know how much of the sky is included in each photo. 
  • Submit multiple observations in one day if PACE is passing overhead more than once (daytime observations only, please).  

Android users: We’ve encountered an issue with the GLOBE Observer app that we are actively working to resolve. If you are unable to download the latest version of the app, please be patient. We will update this news item when the issue is resolved.

Benefits of Participating

In addition to helping scientists on the NASA PACE mission, you will receive a personalized email for each observation aligned with the PACE satellite passing overhead. The email will show you how your observation data compare with the PACE satellite data for the same location. Volunteers who submit observations during the optimal observation window (within 5-minutes of PACE passing overhead) AND complete that observation with all six photos will receive a certificate of recognition.

resources

Just Getting Started?

  • Get Trained! 
    Watch the recording of our recent PACE Clouds Challenge training to learn how to accurately estimate cloud cover percentage, record observations within the critical 5-minute PACE overpass window using the GLOBE Observer app, and review the matched satellite imagery NASA will send back to you. (Esta capacitación también está disponible en español. Ver la grabación.)
  • Tips for Quality Cloud Observations
  • GLOBE Observer: Clouds - Getting Started (video)
    This short video describes how to use the GLOBE Observer app to observe clouds and includes helpful tips.
  • How to Turn on Satellite Flyover Notifications (video)
    This short video tutorial will show you how to turn on satellite flyover notifications for your current location.
  • Cloud Observation Tips & Tricks
    Use this step-by-step guide to high-quality cloud observations, which also includes tips and tricks for cloud identification.

Additional Resources

What is Pace and Why is it Interesting in GLOBE Clouds Data?

The PACE (the Plankton, Aerosol, Cloud, ocean Ecosystem) satellite provides a unique hyperspectral view of the entire planet every 1–2 days designed to reveal invisible information about tiny algae (fish food) in the sea, plants on the land, and particles in the air. 

PACE launched on 8 February 2024 and is now in the phase in which scientists are learning how to use the information it provides to study clouds and aerosols (tiny particles in the atmosphere). PACE measures how clouds and aerosols  absorb and reflect sunlight to provide information about cloud cover and cloud type—key factors in weather and visibility forecasts. This information can also provide insight into how aerosols and clouds interact and how aerosols and clouds affect climate—things that are not well understood.

From the Scientist

“We want to be able to identify whether or not each pixel in a satellite image is a cloud or not, because if it's cloudy we want to determine the properties of that cloud, and if it's not cloudy we want to determine the properties of the atmosphere and surface underneath the cloud. So cloud detection is normally the first step in a satellite data processing stream. However, it is difficult to know objectively how well the cloud detection techniques work, especially near cloud edges and in situations where clouds are broken (given our pixels are about 1.2 km across). So the ground observers will help us to assess that.”—Dr. Andy Sayer (University of Maryland Baltimore County), NASA PACE Satellite

Learn more about PACE and the challenge by watching the August 2026 GO Connect recording: Meet PACE. 

Learn More About Cloud Types and Cover

  • Sky Window
    This resource allows you to cut out the rectangle in the middle of the Sky Window and use the information on the frame to help describe sky conditions and identify clouds.
  • GLOBE Cloud Cover and Estimation Interactive
    This interactive web-based tool allows you to calibrate your eye by practicing cloud-cover estimation using images on the computer. 
  • Estimating Cloud Cover Activity
    In this activity, you create a cloud collage and ask others to guess the percentage of cloud cover (watch video demo). You need only paper (white and blue), scissors, glue or tape, and a marker or pencil for this activity. Expand or adapt this activity by printing photos of the sky and asking participants to identify the cloud coverage.

Having Trouble?

I can’t download the app.

There is a known issue affecting users of newer Android models. We are working on resolving this issue. Check the GLOBE app issues update for current information. 

I can’t find overpass times or receive an alert. 

Check that you have the latest version of GLOBE Observer and that notifications are enabled. You can also use the NASA GLOBE Satellite Overpass Times page to find predicted overpass times in a browser.  

My observation count looks wrong. 

The count on the Clouds landing screen may not update correctly. Check My Observations to see whether your observation is listed.  

My PACE match email hasn’t arrived. 

Please allow 1–2 days for processing and then check your email and My Observations. A match is not guaranteed for every observation.  

My observation is stuck and won’t submit. 

After 15 minutes, check My Observations. If you don’t see your observation there, please wait and try to resubmit the data. The servers may be too busy to accept data or your connection may be poor. If you do see your data in My Observations, we have the data, but the app didn’t receive a confirmation from the server. You can safely delete that observation from the pending queue in the app. 

I tried to send my observation and got an error message (red exclamation mark).

This can happen when you have previously sent your observation, but the acknowledgement from the database that the data have been received doesn’t get back to your device. Since the data are still in the pending queue in the app, if you try to send it again, you’ll get the error and a red exclamation mark. Check your My Observations page for the particular observation with the error. If it’s there, you can delete it from the queue.

My satellite flyover notifications are delayed, and don’t appear 15 minutes before the overpass. 

Some users have noticed this issue on their Android phones when they have activated battery optimization features. Check under your settings, either generally or for the GLOBE Observer app, and make sure you allow unrestricted background usage for the app.