Monthly Archives: March 2016

Night-time Satellite Imagery Helps Identify Rural Electrification

Utilizing night lights imagery from NOAA’s fleet of satellites, the World Bank is analyzing night lights imagery of the world. In a recent blog post, the World Bank has announced the launch of a website which presents maps and analysis of night-lights over India, which can be extended easily to other regions and countries as well. These results are given on the webpage, and the data can be accessed through API also.


India night lights produced by the analysis described below. Source: WorldBank /

NOAA’s DMSP (Defense Meteorological Satellite Program) is the oldest set of satellites monitoring night lights, aided in recent years by observations from the VIIRS (Visible Infrared Imaging Radiometer Suite) sensor onboard the Suomi-NPP satellite (see some more interesting applications of VIIRS here).

At NOAA, the Earth Observation Group (EOG) specialises in the analysis of night-lights imagery. One of the leading scientists and leaders of the EOG group, who has made a career out of analysing night-lights imagery, is Chris Elvidge. Besides many other applications, EOG at NOAA has previously also developed a Night Light Development Index (NLDI) as a “simple, objective, spatially explicit and globally available empirical measurement of human development derived solely from nighttime satellite imagery and population density.” A scientific paper on development of NLDI can be accessed here.

There is an also interesting Masters Thesis from ETH Zurich on “Nighttime lights as proxy for the spatial growth of dense urbanized areas”, and all relevant info is available at the World at Night website.

Finally, here is a really interested detailed article on NASA EarthObservatory detailing how satellites observe night-light imagery.

Using satellite night-lights imagery to study and analyse urban / rural sprawl and growth is a great example of how remote sensing can be used to leverage socio-economical planning and development.

See a previous post about Night-time Imaging and Video from Space.

Another Step Towards Real-time Space Imaging


Near-real time SAR image captured by Sentinel-1A off the coast of Brazil, downlinked to the ground in mere seconds, and processed to image form in just 13 seconds. Image credit: ESA / DLR.

The era of near real-time and real-time optical and radar space imaging is drawing closer and closer. A big step forward in this direction was taken recently by an ESA experiment of a SAR image taken by Setinel-1A, then communicated to an optical communication Technology Demonstration Payload onboard Alphasat via laser beam, which then relayed it to the ground station. This data was then processed and converted to “image” form in just 13 minutes.

This experiment is a precursor towards the establishment of the European Data Relay System (EDRS) SpaceDataHighway, which aims to utilize relay communication satellites to transfer data to and from different satellite / aerial platforms to ground stations at very high speeds using laser communication. Detailed information about the EDRS SpaceDataHighway can be accessed here, here, and here.

I think it is just a matter of a few years before near-real time space imaging (accessible within a few minutes of data acquisition) will be commonplace in the civilian / commercial domain. And that will bring along a lot of new applications of satellite imaging to the fore. Exciting times ahead!


A schematic description of the EDRS SpaceDataHighway. Image credit: ESA.

The Fuss Over P values


xkcd’s “real” interpretation of p-values

The American Statistical Association (ASA) has recently taken the unusual step of announcing a guideline document for preventing the misuse of p-values. They assert that scientists and policy-makers are using the p-value as a black-or-white decision parameter without truly understanding it and without inspecting the overall experiment / methodology / statistical framework. In this statement, the ASA advises researchers to refrain from drawing explicit scientific conclusions or making policy decisions based on just P values. They further advise that as part of scientific statistical analysis, the data analyses, statistical tests, and choices made in calculations should all be described in complete detail.

The ASA’s “statement on p-values: context, process, and purpose” can be accessed here, and the accompanying press release can be seen here.

I don’t want to go into the details of hypothesis testing and p-values here; those interested can take a course in statistical analysis or just scour google, or still, can take my graduate course on Data Analysis for the Earth Sciences.

To improve the conduct and interpretation of quantitative science, ASA has given the following six principles in the guideline document:

  1. P-values can indicate how incompatible the data are with a specified statistical model.
  2. P-values do not measure the probability that the studied hypothesis is true, or the probability that the data were produced by random chance alone.
  3. Scientific conclusions and business or policy decisions should not be based only on whether a p-value passes a specific threshold.
  4. Proper inference requires full reporting and transparency.
  5. A p-value, or statistical significance, does not measure the size of an effect or the importance of a result.
  6. By itself, a p-value does not provide a good measure of evidence regarding a model or hypothesis.

Many interesting and insightful news articles related to this released guideline have been published from different platforms. Nature News contains this directly linked article, and this detailed article from 2014 which discusses the pitfalls of relying too much on P-values. There are engaging  analyses presented in ScienceNews and Inside Higher Ed. RetractionWatch also published an interview with the ASA’s executive director.

I asked my colleague Dr. Asad Ali, an expert in statistical analysis, for his views;  he had this to say:

This p-value has become quite controversial in the last few years. People are abusing it intentionally or miss-using it because of lack of knowledge.

Rejection of a hypothesis does not always mean that it’s wrong, rather it can be also because our evidence (sampled data / observations) is not very representative of the underlying population.

Dr. Asad Ali works in the fields of Bayesian statistics, astrostatistics, and geostatistics, teaching extensive graduate-level courses on these topics at GREL. He is also a part of the eLisa mission data analysis team to observe gravitational waves from space.
To end this blog  post, I can’t resist sharing this brain-wrecking xkcd p-value joke:

A joke for statisticians only

Free NASA Space Travel Posters


NASA JPL has recently released 15 new awesome and inspiring space travel posters. They are downloadable for free in hi-res, and ours to print. The sizes are 20 x 30 inches. The posters include relatively nearby locations such as Mars, and farther-out more exotic planets such as Jupiter’s Galilean moon Europa, and the dwarf planet Ceres, to even planets outside our Solar System, such as Kepler-16b which astonishingly orbits a binary star system.

Check out the posters here:

Challenging the Custodians of Scientific Literature

I have recently been reading some interesting articles regarding the access of scientific literature. One red-hot issue at the center of the current debate is the Sci-Hub website (open at your own legal peril), launched by a neuro-scientist in Russia, who decided to make published research available to everyone, for free. Sci-Hub is also being called the “Pirate Bay of Science”, make what you will of that.

While the debate rages on about the legality of the Sci-Hub webpage, as a researcher, I have often questioned personally, why do researchers have to pay ~$30 for accessing a single paper? Or otherwise, their institute must sign up for institutional access, at exorbitant prices. All this, when the publisher doesn’t even pay a dime to the reviewers, who are the backbone of this whole process. Are the publishers charging this much $$ from their readers for just maintaining the database, their servers, and providing coordinating services? Food for thought…


While reading an expansive recent article on ScienceAlert about Sci-Hub, I found this quote by the founder of Sci-Hub, Alexandra Elbakyan, very poignant:

All papers on their website are written by researchers, and researchers do not receive money from what Elsevier collects. That is very different from the music or movie industry, where creators receive money from each copy sold.

To that, I would like to add that the reviewers, whose dedication of time and effort make the process of peer-review and scientific advancement possible, are also paid nothing.

To add to the discussion about Sci-Hub, here is a very interesting in-depth article on the vision and force behind Sci-Hub.

Following that up, on the side, is a moving article about Aaron Swartz, a boy-genius and a prodigy, who was the founder of RSS feeds, and co-founded Creative Commons and Reddit, among other significant creations on the internet. The life of Aaron Swartz, who committed suicide at 26, is so compelling, I wonder why Hollywood has not made a movie about him yet.

As a footnote, many renowned and wealthy academic institutions like Harvard University, USA, Memorial University of Newfoundland, Canada, Ryerson University, Canada, University of Montreal, Canada, Brock University, Canada, and Helsinki University, Finland, are now finding it hard to afford and keep up with exorbitant journal subscription fees.

I will definitely be writing more about the current state of academic publishing and the access to science and scientific literature in the future on this blog. Look forward to your views in the comments.