News - GLOBE Observer
How to Compare Your Cloud Observations to Satellite Data
One of the most exciting moments in making a cloud observation is receiving your NASA “Satellite-Match” personalized email. The email includes data about your observation, time and location, and it matches it to satellite data obtained at approximately the same time and at your location.
Understanding the Three Parts of Your Satellite Match Table: Overall, Detailed, and Images
For each section, look at the overall comparisons between your report, and the resulting data. Remember, your point of view of the sky (from the ground looking up) is different from the instruments on the satellites (from space looking down). Let's go over what to focus on in each section.
The Overall Section
This section of the table contains satellite names, latitude and longitude, date and time, and total cloud cover reports. In yellow, you will find the geostationary satellite data for your location. This could be from GOES, Himawari, or Meteosat satellites. In blue, you’ll find data gathered from the Aqua satellite. And if that same column is orange, then you will find data from the Terra satellite. Your observations will always appear on the left-hand side, in green.
“Total Cloud Cover” reports from the satellites are a number, while your observations lie in an approximated range. The circle symbols represent a range of observation options to select from (see image below).
Helpful Hint: Use the symbols to see if the satellite reports fall into the same category as your report.
What if the results don’t agree? Cloud cover differences are affected by many variables. Maybe the satellite saw clouds at layers you were not able to detect with your eyes. Perhaps it was hard for you to choose the range of cloud cover. You can try the cloud cover estimation activity, and test your skills with cloud covers created by others!
Take it a step further: Observe data from multiple satellites and examine how much the results vary! If you make cloud observations for multiple days, try to spot a pattern. For example, the satellite values are always within the range you report.
The Detailed Section
This section holds information about the amount and characteristics of observed clouds. This data is divided by the altitude level at the base of the clouds; so clouds with bases lower than 2,000 meters are considered low-level clouds. Clouds with bases between 2,000-6,000 meters are mid-level clouds, while high clouds are those with bases higher than 6,000 meters.
Helpful Hint: You, the observer, are the only one that reports the cloud type for the report – the satellite’s instruments do not. The instruments onboard the satellites do tell you what they observed. However, this information is displayed by divisions in altitude, what is inside the cloud (water droplets, ice crystals, or both), and by opacity!
You can compare your observations to the satellite data and see if they agree in the opacity and cloud cover for that level.
What if the observations don’t agree? Focus on the big picture. Ask yourself which layer had the most clouds reported by all views, or whether the opacity is in agreement through each report. Noticing where the observations agree will give you a better idea as to why there are differences, big or small, and especially when you look at the images in the last section of the report.
The Images Section
Here you will find different sets of images. The satellite images are centered over your location. For geostationary satellites, your location is represented by a dot. These images will also have a red circle marking a 40 kilometer diameter area around your location. For Terra and Aqua, a link to NASA’s visualization program (Worldview) will be included in the email. Based on your data, the Worldview link will be centered around your location, allowing you to zoom in and out, as well as add other data fields. You will also see your own images submitted through the GLOBE Observer app. Your images are incredibly valuable to researchers, who get an on-ground view to better understand observation reports.
Helpful Hint: Look through the satellite images for cloud puffs or thin layers. Just like cumulus clouds are described as puffy, they will also look puffy in satellite images. Thin wispy cirrus clouds look thin in satellite imagery as well.
Take it a step further: The GLOBE Clouds team has produced step-by-step guides on how to interpret satellite images. Use the guides for geostationary satellites, or the MODIS instrument on the Terra and Aqua satellites as appropriate.
What if I have a CALIPSO satellite match? The CALIPSO satellite match is slightly different from the table you receive from the other satellites. You can read more about CALIPSO and how to read that particular satellite match by using our step-by-step guide.
Clouds are a key factor influencing local weather as well as the Earth’s climate system. Satellites can only capture a top-down view of our planet. Your ground observations complement what the satellites cannot see. When you make a GLOBE cloud observation timed to a satellite overpass (within 15 minutes of a satellite observation), then both points of view are matched. Your cloud observations, timed to satellite overpass times, are an important part of the Earth system puzzle NASA is actively building.
About the Author:
Marilé Colón Robles is the project scientist for NASA GLOBE Clouds and the principal investigator of NASA GLOBE CLOUD GAZE based out of the Science Directorate at NASA Langley Research Center with Science Systems and Applications, Inc. Marilé works with scientists on ways to include citizen science data into research. She also works with students and teachers around the world to engage students in real-world STEM activities and in authentic science through The GLOBE Program.