Lewis says keeping tabs on foreign trade requires checking in more frequently. “I used the Planet database because they have a high ‘revisit’ rate,” he says. “Compared to high-res imagery from other providers, their online catalog had about twenty new images since September 2015, when the last high-res images were available online.” Obviously, Sino-Korean relations have changed a lot since September, after another nuclear test in defiance of China and the United States.

The Washington Post reported:

Secretary of State John F. Kerry publicly called on China to end “business as usual” with North Korea. Publicly, Beijing rejected being told by the United States how to handle its client state. Behind the scenes, it appears Beijing was doing just that.

But the Post’s take was based on “anecdotal reports” of Chinese cutbacks beyond a limited set of UN sanctions and, crucially, an expert analysis of one set of photos taken since the nuclear test in January, compared to a set taken a year earlier. Lewis noticed the timestamps on the newer photos: February 13th and 14th, 2016. Those days were a Saturday and a Sunday. Much more important, they were the tail end of the Spring Festival Golden Week, eight days of national and local holidays during which China celebrates its Lunar New Year. “It makes perfect sense there would only be five or six trucks at Dandong in China, or across the river at Sinuiju,” he says. “Hardly anyone is working, compared to the normal business Thursday in last year’s photo.”

By contrast, ten sets of photos taken by Planet satellites since February show an admittedly grainer, but obviously busier picture. The customs lots have been as packed this year as they were last year.

Planet’s online catalog showing the China-North Korea border. Image ©2016 Planet Labs, Inc. cc-by-sa 4.0

The photos might seem too blurry for a layperson to parse, but look again with Lewis’ guidance: “The parking lots on both sides of the borders are still busy with commerce. If the lots were empty, they would be black. Instead, they are mottled with different colored vehicles and containers moving goods in and out of North Korea. It is hard to count individual trucks, but I can assess whether the border crossing is busy or not.”

Andrea Berger, a senior research fellow at the Royal United Services Institute for Defence and Security Studies in London, says it makes sense that despite formal embargoes announced by China’s Ministry of Commerce in April, the number of trucks rolling back and forth has not changed much.

“China is not obligated to curb general trade with North Korea under new sanctions,” Berger says. “It is prohibited from importing a few North Korean commodities such as gold and titanium, but these were only ever a small part of bilateral trade. There are restrictions on more significant commodities like coal as well, but these have major exemptions for ‘livelihood’, which in effect covers the vast majority of trade in these goods.”

The UN sanctions aren’t meant to punish North Korea at large for its obstreperous behavior, but to block specific shipments of coal and metals that could be used in North Korea’s programs to develop nuclear warheads and ballistic missiles. Even those materials aren’t being shut off entirely, as long as Chinese officials feel certain they’re not going to build nuclear missiles.

Stephan Haggard, a professor of Korea-Pacific Studies at the University of California in San Diego, warns against drawing conclusions from a single photo. “Seeing — or not seeing — trucks at the bridge or other crossing at any given point cannot be taken for evidence of anything,” he says, “unless carefully calibrated measurements of traffic have been taken for some time, including at the same time of year, given that trade is seasonal.”

Lewis agrees that despite the appeal of high-resolution satellite photos, what is equally as helpful — if not more so — to analysts is more frequent intel on more areas of interest. “Having one high-resolution picture doesn’t tell you everything,” he says. “Having lots of moderate resolution pictures, on the other hand, is more than good enough to answer the question of whether China cut off North Korea. And the answer is no.”