NEO News

NEO Analysis in 10 Easy Steps

Would you like to explore satellite data yourself? The new NEO analysis tool provides an easy way to compare imagery online and this new blog series highlights different Earth science concepts by pairing an introductory video with an investigation of relevant satellite imagery found here. After you’ve learned the steps, you can try these examples for yourself:

ANALYSIS: PACIFIC LIFE – HOW IS IT RELATED TO OCEAN TEMPERATURE?

ANALYSIS: HOT IN THE CITY

ANALYSIS: REFLECTIONS ON THE BLUE PLANET

Here are the basic steps to follow. Try it now!

Read more

Data-like File Formats: CSV and floating point GeoTIFFs

In addition to the standard file formats that we support in NEO—JPEG, PNG, GeoTIFF, and GoogleEarth—many (not all) datasets support two additional “data-like” formats: CSV (comma-separated values) and floating point GeoTIFF. When you choose one of these formats for download, there are a few details that should be taken into consideration.

  • The values that these files contain have been scaled and resampled for visualization purposes in NEO and should not be considered for rigorous scientific examination. At best they are useful for basic analysis and trend detection but if you are interested in conducting research-level science we recommend that you use the original source data (which are not hosted by NEO, but we can assist you in identifying the source).
  • CSV files can get quite large at full resolution. For example, a 3600×1800 CSV file can get to around 61MB. If your software has difficulty opening a file of that size then please select a smaller resolution (e.g., 1440×720).
  • There are two flavors of CSV available in NEO:
    1. “Regular” CSV which includes the text-only values at the resolution the user specifies. This format is suitable for Excel (2007 and later) and many other applications.
    2. “CSV for Excel” In Excel versions prior to 2007, worksheets could not support more than 256 columns. To remedy this, this format option is resized to 250×125. The first row contains the longitude values for the center of the cell and the first column contains the latitudes.
  • Floating point GeoTIFFs contain 32-bit numerical data along with the geolocation information that is standard for the Geo format. These files can also get large as they are not internally compressed—e.g., a 3600×1800 GeoTIFF can be around 25MB.

These formats are not available by default on our ftp site but if you are interested in obtaining a long time series of a dataset in one of these formats, please contact us and we can perform a customized export to the ftp site in the format you need.

Analysis: Pacific life – how is it related to ocean temperature?

Note that these examples are intended for curious people looking for hands-on Earth data exploration. Primary scientific research will require additional analyses through other methods. For the basics on how to use the NEO tool, see ‘Analysis tool in 10 easy steps’.

Here we explore phytoplankton blooms and their relationship to sea surface temperatures, with background information featured in ClimateBits: Phytoplankton.

Recent studies link warmer waters off the U.S. west coast to more frequent toxic algae blooms, negatively impacting the marine food web and the economy. In 2014-16, the waters off the west coast were unusually warm and were famously dubbed the ‘warm blob’ by the press. The warmer ocean impacted weather on the west coast and was linked to lower fish catches and stressed sea life.

A toxic algae bloom in 2015 extended from California to Alaska resulting in the closure of the Dungeness crab fishery and an economic decline of $100 million, according to the Fisheries of the U.S. Report, 2015. Sea lion strandings increased, including a starving baby sea lion that seated itself at a San Diego restaurant in early 2016, weighing half of what it should for its age according to the Sea World rescue team.

Following the strong El Niño of 2015-16, ocean temperatures off the west coast returned to ‘normal’. Here we use NEO to explore these reports. How do the satellite sea surface temperature records compare before, during, and after the warm anomaly?

Figure 1. North Pacific Sea Surface Temperatures during February 2013 (red), February 2015 (green), February 2017 (blue). Transect values from NW to SE along the U.S. west coast.

A NEO comparison of ocean surface temperatures for the month of February before the warm anomaly in 2013 (red), during the warm anomaly in 2015 (green), and after the warm anomaly in 2017 (blue). Along the entire west coast – from Alaska to the Baja Peninsula – temperatures during the warm blob (February 2015) were roughly 3 degrees C (or 5 degrees F) warmer compared to before (February 2013) and after (February 2017).

Temperatures off of Alaska (Distance ~ 0km along the transect) were around 7C in February 2013 and 2017, but around 10C in 2015. Off of southern California (Distance ~ 2000km), temperatures were around 13C in February 2013 but 16C during the warm blob in 2015. West of the Baja Peninsula (Distance ~ 3500km), temperatures were around 21C in 2013 and 2017, but 25C in 2015.

How do the temperature changes relate to ocean biology measured by satellites?

Figure 2. North Pacific chlorophyll concentrations during February 2013 (red), February 2015 (green), and February 2017 (blue) plotted in a histogram for the area west of California outlined in white.

Chlorophyll concentrations indicate the amount of phytoplankton blooming. More phytoplankton means more food for fish and the rest of the marine food web. In the chlorophyll histogram in Figure 2, chlorophyll during the warm blob in February 2015 (green) had lower values (around 0.1 mg/m3) more frequently than the other two years. The waters were almost 10 times more productive (approaching 0.9 mg/m3) in February 2013 (red) compared to the other two years. Recall that February 2013 had the coolest water.

Usually, cooler surface water means that the water has recently been at depth — below the sunlit surface. Deep water containing unused nutrients can support new phytoplankton blooms. Thus, cooler water is generally associated with higher chlorophyll concentrations. How do the two data sets compare along the west coast before, during, and after the warm blob?

Here we compare sea surface temperature and chlorophyll along a transect from NW to SE off the coast of California for February 2013, 2015, 2017.

Figure 3. Sea surface temperature (red) and chlorophyll (green) plotted along the white transect line in the large panel, from northwest to southeast for February 2013 (left), February 2015 (middle), February 2017 (right) – before, during, and after the warm blob, respectively.

In all of the plots in Figures 3, sea surface temperature and chlorophyll demonstrate their inverse relationship. Cooler, more productive water to the north is contrasted with warmer, less productive water toward the south. The peaks in the chlorophyll (green line) correspond to phytoplankton filaments typically associated with nutrient entrainment along the boundaries of circulation features, such as in the California Current system. Note that over the 2000km transect from northwest to southeast, temperatures changed about 10C and chlorophyll concentrations changed more than an order of magnitude (10x). Also notice that February 2013 (Figure 3, left) had chlorophyll peaks reaching concentrations around 5 mg/m3. During the warm anomaly in 2015, chlorophyll concentrations were never above 0.9 mg/m3. After the demise of the warm blob, sea surface temperatures cooled in 2017 (Figure 3, right) compared to 2015 (Figure 3, middle), chlorophyll concentrations remained low (< 0.9 mg/m3) and were certainly much lower than in 2013.

Diving into the 2017 data a bit more through scatter plots, we can highlight the geographical distributions of different data combinations.

Where are the highest chlorophyll concentrations?

Figure 4. Scatter plot of sea surface temperature (bottom axis) versus chlorophyll (left axis) during February 2017 for the region within the white line. The highest chlorophyll values (magenta box on the scatter plot) are highlighted in magenta on the map. Note that the values at the very top of the plot (74mg/m3) are outliers or artifacts.

Where are the warmest waters within the area outlined in white?

Figure 5. Same plot as Figure 4, with the magenta area highlighting a different distribution of temperature (16-21C) and chlorophyll values (0.05-0.2 mg/m3).

Where are the coolest waters within the area outlined in white?

Figure 6. Same plot as Figure 4 and 5, with the magenta area highlighting a different distribution of temperature (7-10C) and chlorophyll values (0.2-0.8 mg/m3).

Not surprisingly, the coolest waters are in the north; the warmest waters are in the south and the most productive waters with the highest chlorophyll values are next to the coast where nutrients were plentiful. Recall that January and February 2017 was a time of plentiful rain and snow on the west coast (a.k.a. atmospheric rivers that led to much run-off from land).

Note: This blog was written in response to a request for an analysis comparing sea surface temperature and chlorophyll. If there is an analysis you would like to see in this blog, please let us know! 

Analysis: Hot in the city

As the northern hemisphere approaches summer, we explore land surface temperatures that are featured in ClimateBits: Urban Heat Islands.

Note that these examples are intended for curious people looking for hands-on Earth data exploration. Primary scientific research will require additional analyses through other methods. For the basics on how to use the NEO tool, see ‘Analysis tool in 10 easy steps’.

Urban Heat Islands are places on land where buildings, roads, and other impervious surfaces trap more heat than the surrounding rural area. During summer, an urban place like New York City can be 4°C (7°F) or more warmer than surrounding rural areas. Vegetation plays a cooling role through transpiration. Cities such as Minneapolis, Chicago and St. Louis — where most trees were cleared to make way for pavement and development — are urban heat islands surrounded by cooler forests.

Demonstrate seasonal changes

Load March, June and September, 2016 for land surface temperature [day]. These are found under the ‘Land’ category. Note the difference between ‘land surface temperature’ and ‘average land surface temperature’ data sets, the latter being climatology. We use the former in this example. These are MODIS/Terra observations collected since February, 2000 at daily, 8 day and monthly temporal resolution. Here we compare [day] temperatures.

The warmest land is colored yellow; coolest land is colored light blue. Hottest places are in the tropics and during summer in areas where the land is driest. Coldest places are covered in snow and ice. Black areas are missing data — over the ocean or due to cloud cover or lack of sunlight. The values along the white transect on the large map are plotted for March (red), June (green), September (blue).

The white line drawn from south of Lake Michigan east to New York City shows that the transect was about 10°C cooler in March compared to June and September in 2016. As the month of maximum sunlight, June would be expected to be warmest, yet September temperatures were not much cooler due to the thermal inertia of the land.

Compare day/night seasonal changes

Now load March, June and September, 2016 for land surface temperature [night]. Night temperatures are also coldest for places covered in snow and ice, but have important differences from daytime temperatures for warm areas.

The same line drawn from south of Lake Michigan east to New York City corresponds to the plot of nighttime temperatures for March (red), June (green), September (blue). September temperatures were again very close to those in June, especially for the urban areas at either end of the transect (near Chicago and New York City).

Compare urban and rural day/night temperatures

Looking at a weekly map from the end of June, we can compare day and night temperatures with a focus on urban versus rural New York.

Land surface temperature [day] in red and [night] in green for the week of June 26-July 4, 2016. Histograms show temperature distributions around urban New York City (left) compared to rural upstate New York (right).

The first thing to notice is the higher daytime temperatures around New York City (maximum 37°C) compared to upstate New York (maximum 28°C). Second, are the higher nighttime temperatures around New York City (most of values are much greater than 19°C) compared to upstate New York (most of the values are less than 19°C). Notice especially that there is more overlap between daytime and nighttime temperature distributions for New York City. This is the urban heat island effect.

Related Reading

Analysis: Reflections on the Blue Planet

To better engage you on critical Earth science topics, NEO launched a new web-based analysis tool. This Analysis Blog explores NEO data sets used in ClimateBits: Albedo. Albedo is the fraction of incoming solar energy that is immediately reflected back to space.

Note that these examples are intended for curious people looking for hands-on Earth data exploration. Primary scientific research will require additional analyses through other methods. For the basics on how to use the NEO tool, see ‘Analysis tool in 10 easy steps’.

Reflected shortwave radiation

Categorized under ‘Energy’, maps of reflected shortwave radiation show the amount of solar or shortwave energy (in Watts per square meter) reflected by the Earth. These are CERES observations combined with MODIS measurements, available since July, 2006. Brighter colors indicate more reflection while dark blue indicates the least reflection. The brightest, most reflective regions are associated with clouds, snow and ice. Because clouds move quickly, they are best observed in daily maps. The 8 day and monthly composites mute transient weather patterns. More persistent features, such as polar ice caps, can be observed and compared at longer time increments. The least reflective regions are dark surfaces without cloud cover, such as forests and the ocean. The poles are dark during their winters because of the absence of sunlight then.

Reflected Shortwave Radiation (in Watts per square meter). The pale green to white regions show where more sunlight is reflected; dark blue regions are where the least sunlight is reflected.

Land albedo

Categorized under ‘Energy’ as well as ‘Land’, maps of albedo show how reflective land surfaces are from 0, meaning no reflection, to 0.9, indicating nearly all incoming solar energy is reflected. These maps are derived from MODIS measurements, available since February, 2000 at 16 day and monthly composites. Dark blue indicates the least reflection and white indicates the most. Black areas are missing data – over the ocean or due to cloud cover or lack of sunlight.

Land albedo scales from 0 (dark blue) meaning no incoming sunlight reflected to 0.9 (white) meaning almost all sunlight reflected (1 would be all). Black areas mean “no data,” either over ocean or because persistent cloudiness prevented a view of the land surface. Notice the highest albedos are due to ice caps, glaciers and snow-cover.

Comparison: different surfaces

Africa is a continent with the Sahara Desert north of savannah grasslands and then forests with thick vegetation. To see how different land cover impacts albedo and reflected radiation, we compare them during January, 2017. We limit our analysis to the area delineated by the yellow box (below, left). Use Data Probe and Plot transect to explore the whole geographic area, comparing and contrasting values of albedo and reflected radiation.

Left: Map of the region selected as the yellow box. Right: a comparison of albedo and reflected radiation from north to south along the transect (white line).

Notice that albedo and reflected radiation are highest over the Sahara Desert, except for the dark spot associated with the Tibesti mountains in northern Chad. Albedo and reflected radiation decline over the savannah grasslands, which are darker. Farther south, over the tropical rain forest, however, reflected radiation starts to rise while albedo continues to decline – likely due to evapotranspiration that promotes cloud formation.

Left: region selected (white box). Right: scatter plot of albedo versus reflected radiation within that region.

A scatter plot of the transition zone between desert and savannah demonstrates the direct relationship between albedo and reflected radiation.

 

Analysis Tool Development Update

I get plenty of email from users who are still trying to wrestle with the Java version of the analysis tool on the NEO website. (If you are one of those please consult our instructions, but also read on.) I get an equal number asking about the status of a replacement for the Java version.

So, an update is due: We are currently in the process of developing a replacement for the Java analysis tool. It will be 100% HTML/Javascript and will not require any plugins or other software aside from your modern browser. As of now I think I can safely say that it will be ready and deployed on the site in the early part of 2017. Once that is completed, the Java-based tool will be retired permanently.

Thank you all for your continued patience. This has been a long time coming.

Update, February 13, 2017: The new version analysis tool is in place on the site now and ready for testing. I have noticed a few quirks so we are working to address those, but in the meantime, please feel free to test it and let me know how it works for you.

New Dataset: Sea Surface Temperature 1998+ (1 day MWOI)

Sea Surface Temperature (MWOI)

We have just added a new sea surface temperature dataset to replace the similar data from the defunct AMSR-E instrument aboard NASA’s Aqua satellite. This replacement dataset is a composite from multiple microwave-based sensors (also including AMSR-E) but includes a longer temporal span, beginning in 1998 and continuing to the present.

Read more about this dataset and download imagery on NEO.

Special thanks go out to Remote Sensing Systems for their assistance.

New Dataset: UV Index

UV Index

The UV Index is a measure of the intensity of ultraviolet (UV) rays from the Sun. Some exposure to the Sun’s rays is beneficial as it helps our bodies produce vitamin D. But too much exposure to UV rays can have harmful effects. In the short-term, skin exposed to UV rays can burn. A ‘sunburn’ can happen within minutes or over the course of several hours. Over the long term, UV exposure can result in premature aging, skin cancer, and damage to your eyes.

These climatology maps are produced using data collected between October 2004 and January 2011 from the Ozone Monitoring Instrument (OMI) onboard the Aura satellite.

View all the images and read more about this dataset on NEO.

Java and NEO Analysis

If you are a user of the analysis tool in NEO (also known as the Image Composite Explorer, or ICE), you may have noticed that after you installed the latest Java update (Java 7 Update 51) the analysis tool no longer works. Most likely you will see a pop-up error that looks like this:

Java security message

The reason you are seeing this message now is that Oracle has been implementing stricter security measures within Java (which is a good thing) and that means applications that used to work may no longer function. The preferred solution to this is for the application owner (that’s me) to purchase a digital certificate that authenticates the site and that will allow the analysis tool to run in your browser without requiring you to do anything else. However, we do not have that certificate implemented yet (I am working on that). So, in the short term, here is a way to work around this problem.

First, you must be able to access and adjust your Java security settings on your computer. For users who are using computers in a school or an organization that has centralized computer administration, this may be impossible. If that is the case, then there may be no way to get the analysis tool to work until we have the authentication certificate in place.

Locate your Java control panel.

Once the control panel opens, you will see five tabs across the top. When you click on the ‘Security’ tab you will see the following:

Java control panel

From here, click on “Edit Site List” in the lower right and another window will open:

Java add site exception

In this window, click on ‘Add’ and then you can enter the url for the NEO website — http://neo.sci.gsfc.nasa.gov/ — this will give the necessary permissions to the NEO analysis tool so that it can run. Once you have entered the url you will also see a warning about running using HTTP. In this case, NEO is only available via HTTP so you can accept this warning.

After you have added the NEO URL, you may click ‘OK’ to complete the process.

Once you have completed all of these steps, the NEO analysis tool will work for you. You have only granted permissions to the NEO website itself, you have not reduced your security level for any other sites.

I will continue to work to resolve this issue with the certification process so that the above is no longer necessary. Until that time, however, you will need to enable the exception as documented above.

New Dataset: Nitrogen Dioxide

OMI NO2 October 2013

Nitrogen dioxide (NO2) is a gas that occurs naturally in our atmosphere. NO2 plays an important role in the formation of ozone in the air we breathe. Ozone high in the atmosphere helps us. It is like sunscreen, and it protects us from harmful ultraviolet (UV) rays from the Sun. Near the ground though, ozone is a pollutant. It damages our lungs and harms plants, including the plants we eat. Ozone occurs naturally in the air we breathe, but there’s not enough of it to hurt us. Unhealthy levels of ozone form when there is a lot of NO2 in the air. NO2—and ozone—concentrations are usually highest in cities, since NO2 is released into the atmosphere when we burn gas in our cars or coal in our power plants, both things that happen more in cities. Ozone pollution is worse in summer. NO2 is also unhealthy to breathe in high concentrations, such as on busy streets and highways where there are lots of cars and trucks. When driving, it is typically a good idea to keep the car windows rolled up and the car's ventilation set to “recirculate” so as to keep pollution out of the interior of the car. It is also important to reduce outdoor activities like playing or jogging if government officials warn you that air quality will be bad on a certain day.

These maps are produced using data from The Ozone Monitoring Instrument (OMI), on board NASA's Aura satellite and are available in daily, weekly, and monthly composites from October 2004 to the present.

View all the images and read more about this dataset on NEO.

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