If you are a nostalgic person, you will be interested in the historical photos of the places where you lived. Just because of the age, many old photos have not been preserved. And limited by the technical conditions decades ago, it is difficult for you to get a high-definition panoramic view of your hometown city, and you can't overlook your grandparents and the places you once lived from the air. But when you see photos of these cities in the 1960s, you will be surprised. Fifty years ago, Beijing should have known that China's first artificial satellite, Dongfanghong-1, was launched in 1970. Obviously, these photos were not taken by China himself. Seeing this, you may ask? Where were these historical photos found? Do you have any photos of my city? These pictures are all from the US Geological Survey (USGS) picture database. During the Cold War, the United States used spy satellites to take a large number of photos over enemy countries, and China was not spared. These satellite images were declassified in batches in 1990s and early 2000s, and can now be viewed and downloaded for free on the EarthExplorer website of USGS. Here's how to download photos. Log in to the website first, and log in to the Earth Explorer website of the US Geological Survey (USGS): click Register in the upper right corner first, otherwise you will be prompted to log in when downloading the picture. First, we define the area to search by clicking on the map on the right. Taking Fenyang, Shanxi as an example, this paper defines a square area as shown in the figure, and looks for satellite photos related to this area. If the location is wrong, you can drag the anchor point on the right to modify it, or delete the anchor point on the left and add the anchor point again: set the download area. Because the basemap used for positioning on the right uses Google Maps, domestic users may not be able to display it. In this case, you can try to manually add the latitude and longitude anchor points with the Add Coordinates button, and you can query the latitude and longitude coordinates with the Shuijingzhu Universal Map Downloader: The specific way to view the latitude and longitude coordinates is to find the position where you need to get the latitude and longitude in the map, and click the marker point button in my marker bar on the left. Mark the point button, and then click where you need to get the latitude and longitude coordinates on the map. Double-click to view the corresponding point coordinates. Obtaining latitude and longitude coordinates can obtain the complete latitude and longitude coordinates of four points in turn, and then add latitude and longitude anchor points according to the obtained coordinates. Add latitude and longitude anchor settings to download data. Then we can click on the dataset to set the data and select the database. Select the database to search. The declassified photos during the Cold War mainly concentrated in the declassified data database. We expand it and check declass 1( 1996). This database is mainly strip-shaped push-broom satellite photos, and the shooting time is concentrated in the late 1960s. Declass 2 (2002) is mostly framed photos, taken in the early 1970s. Declassis3 (2013) has few photos. Let's take declass 1( 1996) as an example. Click additional conditions to enter the next step, and then select some parameters for further screening. Because not all photos can be downloaded for free, and there is no need to look at the photos with low resolution, we set the exclusion of photos with low resolution and pay. Select HD, downloadable and other parameters as shown above. We limit the camera resolution to stereo height and the downloadable to Yes, so that we can directly filter out high-definition and downloadable photos. Click the result to get the result. The query result is shown in the above figure. We see the filtering results in the list on the left, and the result list will show the shooting time and other parameters of each photo. Click the fifth icon with a green arrow to download. Look at the location of the results, but how to determine the coverage of these photos? We can click on the footprint icon to get the location of the photo on the earth. For example, in the following picture, I can preview which area of the earth they cover by clicking on the footprint icons of the two pictures. The advantage of viewing the location is that if you find that the area you need to search has only a little intersection with the photo, you don't need to download it, because at the boundary of the area, the photo is always not so clear, especially when the area you need to view appears at both ends of the photo, lens distortion will lead to extremely unclear picture. In addition, it should be noted that the photo coverage area is only a reference, and it can't completely coincide with the Google basemap on the right, so sometimes there is an error between the downloaded photos and the imagination, which needs to be explored and tried through continuous downloading and viewing. Download the map and then you can download it. Each photo package ranges from a few hundred meters to a few grams, which is very huge. Sometimes it takes a long time to start downloading. If not, consider refreshing or reopening the webpage. Download the map, download the photo package, and decompress. Because each photo is too big, most of them are divided into 3~4 photos, and each file is still several hundred meters. It should be noted that some photos are opposite and need to be flipped manually. Download the map, download the map to view, and then you can happily zoom in and out to see the photos. You can change the database and adjust the parameters yourself to explore. Sometimes it takes some luck to find the perfect photo. After all, not all photos can meet sunny days, and it is common that the focus is not accurate or the picture is biased. The village above shows the village where my father was born. The castle walls are still intact, and you can find the old yard at home. The Yellow River at the junction of Shanxi, Shaanxi and Mongolia has clear topographical and hydrological characteristics, and the conclusions of Hong Kong Kowloon Peninsula, Shenzhen, Luohu, Shenzhen Bay, Nanshan, Shekou and Fenyang in the 1960s are marked with comparison areas between the past and the present. At present, the highest resolution of decrypted domestic historical data has reached 0.6m in some areas, and most areas are covered with1.8-2.7m image data. Since most of the historical images of keyhole satellites are taken by retro cameras, the obtained image data are black and white panchromatic images, and interested friends can try it themselves.