Google has come up with a way to overcome the ad-targeting gap between mobile web visitors and mobile app users, according to people familiar with the matter.

The online ad giant is set to begin testing a new method of targeting tablet and smartphone users that connects the separate tracking mechanisms that follow what people do on the mobile web and in mobile apps respectively, the people said. Until now, advertisers have usually been forced to treat individual mobile users as two unconnected people, depending on whether they are using a mobile browser or apps.

A Google spokesman confirmed the effort. "As an alternative to less transparent methods, we're doing some tests to help businesses run consistent ad campaigns across a device's mobile browser and mobile apps, using existing anonymous identifiers, while enabling people to use the established privacy controls on Android and iOS," the spokesman said in an email.

The targeting method relies on Google's two-million-plus network of third-party sites and its mobile app ad network AdMob, which is able to track and serve ads to users of hundreds of thousands of mobile apps across Apple's iOS and Google's Android mobile operating systems.

Almost a year ago Google made headlines when word leaked that the company was prepping a replacement for the cookie, the primary technology used to track web users from site to site and aim certain ads at them. This new mobile ad-targeting method is not that replacement. Instead Google is taking the cookie dropped in a mobile web browser and connecting it with the mobile app equivalent of a cookie. Once those are connected, Google will be able to show the same ads to consumers whether they're using a mobile browser or an app, or recognize consumers who saw one ad in an app and show them a follow-up ad on a mobile site.

Google execs have claimed in private meetings that the new targeting method is more persistent and has better coverage than the company's existing cookies, according to the people familiar with the matter. The new mobile ad-targeting method doesn't involve individuals' personal information, and people will still be able to opt out of tracking on either or both the mobile web or apps, the said.

Over the past few weeks Google has begun inviting a number of automated ad-buying companies to a private beta program this fall to test the new ad-targeting method on Google's ad exchange and elsewhere. The test will let advertisers treat their mobile target audiences as unified groups instead of setting up separate mobile browser and app campaigns.

The new mobile ad-targeting method could help Google to future-proof its ad-tech business as online audiences move to mobile -- and as growing mobile powers like Facebook and Twitter edge into the Google-dominated domain of selling ads on other publishers' sites and apps.

Cookies have become an endangered technology as more people move to mobile. On smartphones and tablets, cookies only work in mobile web browsers, which mean they are blind to any activity that happens in mobile apps.

The cookie's mobile limitations has opened the door to companies like Facebook and Twitter, which are able to anchor people's identities to registered user accounts and connect them across sites and apps. Both companies could use that ability to more accurately target people across mobile web, mobile apps and even desktop web. Facebook and Twitter already target people with ads on the social networks based on the third-party sites -- and in Facebook's case, apps -- they visit. But the companies have also begun selling ads on other publishers' mobile properties. That's Google's turf.

Google is expected to take in roughly 50% of the $32.71 billion to be spent on mobile ads worldwide this year, according to eMarketer estimates. Facebook is projected to follow at 22%, a steep climb from the social network's 5% share two years ago.

In order to fend off Facebook's mobile advance, Google may need to assure advertisers that it can target audiences across mobile web and mobile app with the same accuracy as Facebook, which can authenticate a mobile web visitor and a mobile app user as one and the same.

One limit of Google's new system, which will work on Apple's iPad and iPhone as well as tablets and smartphones running Google's Android mobile operating system, is that it cannot follow people across multiple devices. Google won't be able to trace someone from their iPad, for example, to their iPhone or other smartphone.