Conclusions

We used a variety of aerial and satellite sensors to analyze the selected islands and reefs in the South China Sea. Each study site revealed at least one capability or limitation associated with overhead imaging. The analysis of Mischief Reef demonstrated how high-resolution aerial images were needed to detect and assess the controversial activities there. Moderate-resolution, panchromatic imagery from satellites proved to be limited in monitoring specific activities at Mischief Reef, but it was useful for ship detection and synoptic analysis. The study of Thitu Island demonstrated the value of radar imagery for detecting large-scale infrastructure independent of light conditions or cloud coverage. The aerial photos showed smaller structures such as the individual buildings and observation tower. The accidental discovery of Chinese-occupied Subi Reef in the Radarsat-1 image was a realistic example on how radar imagery could be used as a detection tool. In addition, the analysis showed how coarse resolution features from satellite imagery could be correlated with high-resolution aerial images of the same feature.

The examination of Commodore Reef highlighted the limitations associated with the exclusive use of moderate-resolution, panchromatic imagery. Even though the IRS-1C satellite provided a unique bird’s eye view, it was partially obscured by cloud cover and it did not offer enough spatial detail to verify human occupation of the reef. It did, however, show a few "blips" of possible human occupation that could be examined more closely with higher resolution imagery. Alicoa Annie and Yuan Anha served as controls for the study. The image analysis of these two large reefs with no known occupants came up with no evidence of physical occupation. This suggests that such imagery may be useful for dispelling false allegations of physical occupation and verifying the absence of structures on disputed reefs.

In addition to obtaining empirical results from the study of selected islands and reefs, we also derived results from the different types of remote sensing systems that were used. Table 3 charts the strengths and weaknesses of four general types of aerial and satellite imaging sensors. The assessment is based on the technical and operational utility of each sensor for monitoring the South China Sea specifically. The fourth type, high-resolution satellite imaging, was not used in this study, but its strengths and weaknesses can be extrapolated from high-resolution aerial imaging and moderate-resolution satellite imaging.

From Table 3, we can devise an imaging strategy optimized for monitoring the South China Sea. The overall technical objective would be to monitor all civilian and military activity in the area without provoking an armed incident. To do this, the imaging strategy would have to rely on satellite imaging as much as possible; it is the only platform that can scan the entire South China Sea on a routine basis for ship and island activity. And in contrast with aircraft, imaging satellites can operate from a safe altitude without the risk of being misinterpreted as a fighter-bomber.

Moderate-resolution, radar imaging satellites are the best space-based system for performing routine search missions over the South China Sea. Unaffected by adverse weather, radar imaging satellites are the only systems capable of searching for controversial activities that may deliberately use cloud cover as a screen. Radar images from satellites such as Radarsat-1 are well suited for detecting the large ships and outposts that have been observed in the South China Sea. If the images are delivered within 8-72 hours of acquisition, these images could provide early warning of controversial or prohibited activity, whether civilian or military.

Table 3: The strengths and weaknesses of aerial and satellite imaging for monitoring the South China Sea.

Any activity detected in a radar image would most likely appear as a fairly coarse blip. Consequently, higher resolution images would be needed to investigate further. To facilitate the creation of a stable monitoring regime, commercial imaging satellites would be the preferred "close look" platform because the images could be acquired from a safe, remote vantage point, transmitted to a central image archive, and shared with all claimant states and other interested parties.

If such images are unavailable in a timely fashion due to the orbital position of the satellite, the tasking load, or cloud coverage, aerial imaging would be the next viable option for investigating any suspect features found in the radar satellite sweep. To minimize the risk of vulnerability and armed confrontation, the aerial imaging should be done using visibly unarmed aircraft flying around the suspect site at maximum possible stand-off distances. To maximize the degree of transparency in the South China Sea, the aerial data should be shared in a cooperative manner so that claimant states and interested parties can independently assess the observed activity. Such sharing could build on the precedent established by the Philippines’ routine release of aerial images of South China Sea sites.

Our remote sensing study shows that aerial and satellite imaging can provide timely, substantive information on ships, structures, and activities in the South China Sea. With the devised optimal monitoring strategy, future studies can now consider verification provisions for specific political agreements tailored to the capabilities and limitations of aerial and satellite imaging. All of the necessary aerial and satellite imaging platforms for South China Sea monitoring are scheduled to be in place by the year 2000. From that point onward, a formal monitoring regime optimized for the South China Sea will be technically feasible. Whether such a regime will be realized will ultimately depend on multilateral agreement to an interim or permanent solution to the Spratly conflict.

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